support-v7:24.2.0中的新工具類DiffUtil的使用方法

本文轉載自：http://blog.csdn.net/zxt0601/article/details/52562770

一 概述

DiffUtil是support-v7:24.2.0中的新工具類，它用來比較兩個數據集，尋找出舊數據集-》新數據集的最小變化量。 
說到數據集，相信大家知道它是和誰相關的了，就是我的最愛，RecyclerView。 
就我使用的這幾天來看，它最大的用處就是在RecyclerView刷新時，不再無腦mAdapter.notifyDataSetChanged()。 
以前無腦mAdapter.notifyDataSetChanged()有兩個缺點：

1. 不會觸發RecyclerView的動畫（刪除、新增、位移、change動畫）
2. 性能較低，畢竟是無腦的刷新了一遍整個RecyclerView , 極端情況下：新老數據集一模一樣，效率是最低的。

使用DiffUtil後，改爲如下代碼：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.DiffResult</span> diffResult = DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.calculateDiff</span>(new DiffCallBack(mDatas, newDatas), true)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
diffResult<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dispatchUpdatesTo</span>(mAdapter)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

它會自動計算新老數據集的差異，並根據差異情況，自動調用以下四個方法

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">adapter<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.notifyItemRangeInserted</span>(position, count)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
adapter<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.notifyItemRangeRemoved</span>(position, count)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
adapter<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.notifyItemMoved</span>(fromPosition, toPosition)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
adapter<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.notifyItemRangeChanged</span>(position, count, payload)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

顯然，這個四個方法在執行時都是伴有RecyclerView的動畫的，且都是定向刷新方法，刷新效率蹭蹭的上升了。 
老規矩，先上圖，

圖一是無腦mAdapter.notifyDataSetChanged()的效果圖，可以看到刷新交互很生硬，Item突然的出現在某個位置： 

圖二是使用DiffUtils的效果圖，最明顯的是有插入、移動Item的動畫： 
 
轉成GIF有些渣，下載文末Demo運行效果更佳哦。

本文將包含且不僅包含以下內容：

1 先介紹DiffUtil的簡單用法，實現刷新時的“增量更新”效果。（“增量更新”是我自己的叫法） 
2 DiffUtil的高級用法，在某項Item只有內容(data)變化，位置(position)未變化時，完成部分更新（官方稱之爲Partial bind，部分綁定）。 
3 瞭解到 RecyclerView.Adapter還有public void onBindViewHolder(VH holder, int position, List<Object> payloads)方法，並掌握它。 
4 在子線程中計算DiffResult，在主線程中刷新RecyclerView。 
5 少部分人不喜歡的notifyItemChanged()導致Item白光一閃的動畫 如何去除。 
6 DiffUtil部分類、方法 官方註釋的漢化

---

二 DiffUtil的簡單用法

前文也提到，DiffUtil是幫助我們在刷新RecyclerView時，計算新老數據集的差異，並自動調用RecyclerView.Adapter的刷新方法，以完成高效刷新並伴有Item動畫的效果。 
那麼我們在學習它之前要先做一些準備工作，先寫一個普通青年版，無腦notifyDataSetChanged()刷新的Demo。 
1 一個普通的JavaBean，但是實現了clone方法，僅用於寫Demo模擬刷新用，實際項目不需要，因爲刷新時，數據都是從網絡拉取的。:

<code class="hljs php has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">TestBean</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Cloneable</span> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String name;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String desc;
    ....<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//get set方法省略</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//僅寫DEMO 用 實現克隆方法</span>
    @Override
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> TestBean <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">clone</span>() throws CloneNotSupportedException {
        TestBean bean = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
            bean = (TestBean) super.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">clone</span>();
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> bean;
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul>

2 實現一個普普通通的RecyclerView.Adapter。

<code class="hljs axapta has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DiffAdapter</span> <span class="hljs-inheritance" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span></span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">RecyclerView</span>.<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Adapter</span><<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DiffAdapter</span>.<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DiffVH</span>> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> String TAG = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"zxt"</span>;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<TestBean> mDatas;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Context mContext;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> LayoutInflater mInflater;

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> DiffAdapter(Context mContext, List<TestBean> mDatas) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.mContext = mContext;
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.mDatas = mDatas;
        mInflater = LayoutInflater.from(mContext);
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> setDatas(List<TestBean> mDatas) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.mDatas = mDatas;
    }

    @Override
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> DiffVH onCreateViewHolder(ViewGroup parent, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> viewType) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DiffVH(mInflater.inflate(R.layout.item_diff, parent, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>));
    }

    @Override
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> onBindViewHolder(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> DiffVH holder, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> position) {
        TestBean bean = mDatas.get(position);
        holder.tv1.setText(bean.getName());
        holder.tv2.setText(bean.getDesc());
        holder.iv.setImageResource(bean.getPic());
    }

    @Override
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> getItemCount() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mDatas != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> ? mDatas.size() : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
    }

    <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DiffVH</span> <span class="hljs-inheritance" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span></span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">RecyclerView</span>.<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ViewHolder</span> {</span>
        TextView tv1, tv2;
        ImageView iv;

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> DiffVH(View itemView) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(itemView);
            tv1 = (TextView) itemView.findViewById(R.id.tv1);
            tv2 = (TextView) itemView.findViewById(R.id.tv2);
            iv = (ImageView) itemView.findViewById(R.id.iv);
        }
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li></ul>

3 Activity代碼：

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MainActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">AppCompatActivity</span> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<TestBean> mDatas;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> RecyclerView mRv;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> DiffAdapter mAdapter;

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onCreate</span>(Bundle savedInstanceState) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        mRv = (RecyclerView) findViewById(R.id.rv);
        mRv.setLayoutManager(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> LinearLayoutManager(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>));
        mAdapter = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DiffAdapter(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, mDatas);
        mRv.setAdapter(mAdapter);
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">initData</span>() {
        mDatas = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<>();
        mDatas.add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TestBean(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"張旭童1"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android"</span>, R.drawable.pic1));
        mDatas.add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TestBean(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"張旭童2"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Java"</span>, R.drawable.pic2));
        mDatas.add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TestBean(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"張旭童3"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"背鍋"</span>, R.drawable.pic3));
        mDatas.add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TestBean(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"張旭童4"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"手撕產品"</span>, R.drawable.pic4));
        mDatas.add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TestBean(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"張旭童5"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"手撕測試"</span>, R.drawable.pic5));
    }

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * 模擬刷新操作
     *
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> view
     */</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onRefresh</span>(View view) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
            List<TestBean> newDatas = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<>();
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (TestBean bean : mDatas) {
                newDatas.add(bean.clone());<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//clone一遍舊數據 ，模擬刷新操作</span>
            }
            newDatas.add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TestBean(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"趙子龍"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"帥"</span>, R.drawable.pic6));<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//模擬新增數據</span>
            newDatas.get(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>).setDesc(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android+"</span>);
            newDatas.get(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>).setPic(R.drawable.pic7);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//模擬修改數據</span>
            TestBean testBean = newDatas.get(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//模擬數據位移</span>
            newDatas.remove(testBean);
            newDatas.add(testBean);
            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//別忘了將新數據給Adapter</span>
            mDatas = newDatas;
            mAdapter.setDatas(mDatas);
            mAdapter.notifyDataSetChanged();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//以前我們大多數情況下只能這樣</span>
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }

}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li></ul>

很簡單，只不過在構建新數據源newDatas時，是遍歷老數據源mDatas，調用每個data的clone()方法，確保新老數據源雖然數據一致，但是內存地址（指針不一致），這樣在後面修改newDatas裏的值時，不會牽連mDatas裏的值被一起改了。

4 activity_main.xml 刪掉了一些寬高代碼，就是一個RecyclerView和一個Button用於模擬刷新。:

<code class="hljs xml has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-pi" style="color: rgb(0, 102, 102); box-sizing: border-box;"><?xml version="1.0" encoding="utf-8"?></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">RelativeLayout</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">xmlns:android</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"http://schemas.android.com/apk/res/android"</span>
></span>

    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">android.support.v7.widget.RecyclerView
</span>        <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"@+id/rv"</span> /></span>

    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">Button
</span>        <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"@+id/btnRefresh"</span>
        <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_alignParentRight</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>
        <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:onClick</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"onRefresh"</span>
        <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:text</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"模擬刷新"</span> /></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">RelativeLayout</span>></span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul>

以上是一個普通青年很容易寫出的，無腦notifyDataSetChanged()的demo，運行效果如第一節圖一。 
但是我們都要爭做文藝青年，so

下面開始進入正題，簡單使用DiffUtil，我們需要且僅需要額外編寫一個類。

想成爲文藝青年，我們需要實現一個繼承自DiffUtil.Callback的類，實現它的四個abstract方法。 
雖然這個類叫Callback，但是把它理解成：定義了一些用來比較新老Item是否相等的契約(Contract)、規則(Rule)的類， 更合適。

DiffUtil.Callback抽象類如下：

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Callback</span> {</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getOldListSize</span>();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//老數據集size</span>

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getNewListSize</span>();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//新數據集size</span>

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">areItemsTheSame</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldItemPosition, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> newItemPosition);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//新老數據集在同一個postion的Item是否是一個對象？（可能內容不同，如果這裏返回true，會調用下面的方法）</span>

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">areContentsTheSame</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldItemPosition, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> newItemPosition);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//這個方法僅僅是上面方法返回ture纔會調用，我的理解是隻有notifyItemRangeChanged()纔會調用，判斷item的內容是否有變化</span>

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//該方法在DiffUtil高級用法中用到 ，暫且不提</span>
        <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Nullable</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Object <span class="hljs-title" style="box-sizing: border-box;">getChangePayload</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldItemPosition, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> newItemPosition) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
        }
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul>

本Demo如下實現DiffUtil.Callback，核心方法配有中英雙語註釋（說人話就是，翻譯了官方的英文註釋，方便大家更好理解）。

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
 * 介紹：核心類 用來判斷 新舊Item是否相等
 * 作者：zhangxutong
 * 郵箱：[email protected]
 * 時間： 2016/9/12.
 */</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DiffCallBack</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DiffUtil</span>.<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Callback</span> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<TestBean> mOldDatas, mNewDatas;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//看名字</span>

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">DiffCallBack</span>(List<TestBean> mOldDatas, List<TestBean> mNewDatas) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.mOldDatas = mOldDatas;
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.mNewDatas = mNewDatas;
    }

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//老數據集size</span>
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getOldListSize</span>() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mOldDatas != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> ? mOldDatas.size() : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
    }

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//新數據集size</span>
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getNewListSize</span>() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mNewDatas != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> ? mNewDatas.size() : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
    }

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * Called by the DiffUtil to decide whether two object represent the same Item.
     * 被DiffUtil調用，用來判斷 兩個對象是否是相同的Item。
     * For example, if your items have unique ids, this method should check their id equality.
     * 例如，如果你的Item有唯一的id字段，這個方法就 判斷id是否相等。
     * 本例判斷name字段是否一致
     *
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> oldItemPosition The position of the item in the old list
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> newItemPosition The position of the item in the new list
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @return</span> True if the two items represent the same object or false if they are different.
     */</span>
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">areItemsTheSame</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldItemPosition, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> newItemPosition) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mOldDatas.get(oldItemPosition).getName().equals(mNewDatas.get(newItemPosition).getName());
    }

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * Called by the DiffUtil when it wants to check whether two items have the same data.
     * 被DiffUtil調用，用來檢查 兩個item是否含有相同的數據
     * DiffUtil uses this information to detect if the contents of an item has changed.
     * DiffUtil用返回的信息（true false）來檢測當前item的內容是否發生了變化
     * DiffUtil uses this method to check equality instead of {@link Object#equals(Object)}
     * DiffUtil 用這個方法替代equals方法去檢查是否相等。
     * so that you can change its behavior depending on your UI.
     * 所以你可以根據你的UI去改變它的返回值
     * For example, if you are using DiffUtil with a
     * {@link android.support.v7.widget.RecyclerView.Adapter RecyclerView.Adapter}, you should
     * return whether the items' visual representations are the same.
     * 例如，如果你用RecyclerView.Adapter 配合DiffUtil使用，你需要返回Item的視覺表現是否相同。
     * This method is called only if {@link #areItemsTheSame(int, int)} returns
     * {@code true} for these items.
     * 這個方法僅僅在areItemsTheSame()返回true時，才調用。
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> oldItemPosition The position of the item in the old list
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> newItemPosition The position of the item in the new list which replaces the
     *                        oldItem
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @return</span> True if the contents of the items are the same or false if they are different.
     */</span>
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">areContentsTheSame</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldItemPosition, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> newItemPosition) {
        TestBean beanOld = mOldDatas.get(oldItemPosition);
        TestBean beanNew = mNewDatas.get(newItemPosition);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!beanOld.getDesc().equals(beanNew.getDesc())) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果有內容不同，就返回false</span>
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (beanOld.getPic() != beanNew.getPic()) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果有內容不同，就返回false</span>
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//默認兩個data內容是相同的</span>
    }
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li></ul>

註釋張寫了這麼詳細的註釋+簡單的代碼，相信一眼可懂。 
然後在使用時，註釋掉你以前寫的notifyDatasetChanged()方法吧，替換成以下代碼：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">//文藝青年新寵
//利用DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.calculateDiff</span>()方法，傳入一個規則DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Callback</span>對象，和是否檢測移動item的 boolean變量，得到DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.DiffResult</span> 的對象

DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.DiffResult</span> diffResult = DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.calculateDiff</span>(new DiffCallBack(mDatas, newDatas), true)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

//利用DiffUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.DiffResult</span>對象的dispatchUpdatesTo（）方法，傳入RecyclerView的Adapter，輕鬆成爲文藝青年

diffResult<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dispatchUpdatesTo</span>(mAdapter)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

//別忘了將新數據給Adapter
mDatas = newDatas<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
mAdapter<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDatas</span>(mDatas)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>

講解：

步驟一

在將newDatas 設置給Adapter之前，先調用DiffUtil.calculateDiff()方法，計算出新老數據集轉化的最小更新集，就是DiffUtil.DiffResult對象。 
DiffUtil.calculateDiff()方法定義如下： 
第一個參數是DiffUtil.Callback對象， 
第二個參數代表是否檢測Item的移動，改爲false算法效率更高，按需設置，我們這裏是true。

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> DiffResult <span class="hljs-title" style="box-sizing: border-box;">calculateDiff</span>(Callback cb, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> detectMoves)</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

步驟二

然後利用DiffUtil.DiffResult對象的dispatchUpdatesTo（）方法，傳入RecyclerView的Adapter，替代普通青年才用的mAdapter.notifyDataSetChanged()方法。 
查看源碼可知，該方法內部，就是根據情況調用了adapter的四大定向刷新方法。

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">dispatchUpdatesTo</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> RecyclerView.Adapter adapter) {
            dispatchUpdatesTo(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ListUpdateCallback() {
                <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onInserted</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> position, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> count) {
                    adapter.notifyItemRangeInserted(position, count);
                }

                <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onRemoved</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> position, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> count) {
                    adapter.notifyItemRangeRemoved(position, count);
                }

                <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onMoved</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> fromPosition, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> toPosition) {
                    adapter.notifyItemMoved(fromPosition, toPosition);
                }

                <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onChanged</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> position, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> count, Object payload) {
                    adapter.notifyItemRangeChanged(position, count, payload);
                }
            });
        }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>

小結：

所以說，DiffUtil不僅僅只能和RecyclerView配合，我們也可以自己實現ListUpdateCallback接口的四個方法去做一些事情。（我暫時不負責任隨便一項想，想到可以配合自己項目裏的九宮格控件？或者優化我上篇文章寫的NestFullListView？小安利，見 ListView、RecyclerView、ScrollView裏嵌套ListView 相對優雅的解決方案:http://blog.csdn.net/zxt0601/article/details/52494665）

至此，我們已進化成文藝青年，運行效果和第一節圖二基本一致， 
唯一不同的是此時adapter.notifyItemRangeChanged()會有Item白光一閃的更新動畫 （本文Demo的postion爲0的item）。 這個Item一閃的動畫有人喜歡有人恨，不過都不重要了， 
因爲當我們學會了第三節的DiffUtil搞基用法，你愛不愛這個ItemChange動畫，它都將隨風而去。（不知道是不是官方bug） 
效果就是第一節的圖二，我們的item0其實圖片和文字都變化了，但是這個改變並沒有伴隨任何動畫。 
讓我們邁向 文藝青年中的文藝青年 之路。

---

三 DiffUtil的高級用法

理論：

高級用法只涉及到兩個方法， 
我們需要分別實現DiffUtil.Callback的 
public Object getChangePayload(int oldItemPosition, int newItemPosition)方法， 
返回的Object就是表示Item改變了哪些內容。

再配合RecyclerView.Adapter的 
public void onBindViewHolder(VH holder, int position, List<Object> payloads)方法， 
完成定向刷新。（成爲文青中的文青，文青青。） 
敲黑板，這是一個新方法，注意它有三個參數，前兩個我們熟，第三個參數就包含了我們在getChangePayload（）返回的Object。

好吧，那我們就先看看這個方法是何方神聖： 
在v7-24.2.0的源碼裏，它長這個樣子：

<code class="hljs applescript has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">        /**
         * Called <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">by</span> RecyclerView <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> display <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> data <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> specified position. This method
         * should update <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-property" style="box-sizing: border-box;">contents</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> {@link ViewHolder<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#itemView} to reflect the item at</span>
         * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">given</span> position.
         * <p>
         * Note <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">that</span> unlike {@link android.widget.ListView}, RecyclerView will <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> call this method
         * again <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> position <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-property" style="box-sizing: border-box;">item</span> changes <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> data <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span> unless <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-property" style="box-sizing: border-box;">item</span> itself <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span>
         * invalidated <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">or</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> new position cannot be determined. For this reason, you should only
         * use <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <code>position</code> parameter <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> acquiring <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> related data <span class="hljs-property" style="box-sizing: border-box;">item</span> inside
         * this method <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> should <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> keep a <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">copy</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">it</span>. If you need <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> position <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> an <span class="hljs-property" style="box-sizing: border-box;">item</span> later
         * <span class="hljs-function_start" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">on</span></span> (e.g. <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> a click listener), use {@link ViewHolder<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#getAdapterPosition()} which will</span>
         * have <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> updated adapter position.
         * <p>
         * Partial bind vs full bind:
         * <p>
         * The payloads parameter <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> a merge <span class="hljs-type" style="box-sizing: border-box;">list</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">from</span> {@link <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#notifyItemChanged(int, Object)} or</span>
         * {@link <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#notifyItemRangeChanged(int, int, Object)}.  If the payloads list is not empty,</span>
         * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> ViewHolder <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> currently bound <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> old data <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> Adapter may <span class="hljs-command" style="box-sizing: border-box;">run</span> an efficient partial
         * update using <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> payload info.  If <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> payload <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> empty,  Adapter must <span class="hljs-command" style="box-sizing: border-box;">run</span> a full bind.
         * Adapter should <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> assume <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">that</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> payload passed <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> notify methods will be received <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">by</span>
         * onBindViewHolder().  For example when <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> view <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> attached <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> screen, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span>
         * payload <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> notifyItemChange() will be simply dropped.
         *
         * @param holder The ViewHolder which should be updated <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> represent <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-property" style="box-sizing: border-box;">contents</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span>
         *               <span class="hljs-property" style="box-sizing: border-box;">item</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">given</span> position <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> data <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>.
         * @param position The position <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-property" style="box-sizing: border-box;">item</span> within <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> adapter's data <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>.
         * @param payloads A non-null <span class="hljs-type" style="box-sizing: border-box;">list</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> merged payloads. Can be empty <span class="hljs-type" style="box-sizing: border-box;">list</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> requires full
         *                 update.
         */
        public void onBindViewHolder(VH holder, int position, List<Object> payloads) {
            onBindViewHolder(holder, position);
        }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li></ul>

原來它內部就僅僅調用了兩個參數的onBindViewHolder(holder, position) ，（題外話，哎喲喂，我的NestFullListView 的Adapter也有幾分神似這種寫法，看來我離Google大神又近了一步） 
看到這我才明白，其實onBind的入口，就是這個方法，它纔是和onCreateViewHolder對應的方法， 
源碼往下翻幾行可以看到有個public final void bindViewHolder(VH holder, int position)，它內部調用了三參的onBindViewHolder。 
關於RecyclerView.Adapter 也不是三言兩句說的清楚的。（其實我只掌握到這裏） 
好了不再跑題，回到我們的三參數的onBindViewHolder(VH holder, int position, List<Object> payloads)，這個方法頭部有一大堆英文註釋，我一直覺得閱讀這些英文註釋對理解方法很有用處，於是我翻譯了一下，

翻譯：

由RecyclerView調用 用來在在指定的位置顯示數據。 
這個方法應該更新ViewHolder裏的ItemView的內容，以反映在給定的位置 Item（的變化）。 
請注意，不像ListView，如果給定位置的item的數據集變化了，RecyclerView不會再次調用這個方法，除非item本身失效了（invalidated ） 或者新的位置不能確定。 
出於這個原因,在這個方法裏，你應該只使用 postion參數 去獲取相關的數據item，而且不應該去保持 這個數據item的副本。 
如果你稍後需要這個item的position，例如設置clickListener。應該使用 ViewHolder.getAdapterPosition()，它能提供 更新後的位置。 
（二筆的我看到這裏發現 這是在講解兩參的onbindViewHolder方法 
下面是這個三參方法的獨特部分：） 
**部分(partial)綁定**vs完整(full)綁定 
payloads 參數 是一個從（notifyItemChanged(int, Object)或notifyItemRangeChanged(int, int, Object)）裏得到的合併list。 
如果payloads list 不爲空，那麼當前綁定了舊數據的ViewHolder 和Adapter， 可以使用 payload的數據進行一次 高效的部分更新。 
如果payload 是空的，Adapter必須進行一次完整綁定（調用兩參方法）。 
Adapter不應該假定（想當然的認爲） 在那些notifyxxxx通知方法傳遞過來的payload， 一定會在 onBindViewHolder()方法裏收到。（這一句翻譯不好 QAQ 看舉例就好） 
舉例來說，當View沒有attached 在屏幕上時，這個來自notifyItemChange()的payload 就簡單的丟掉好了。 
payloads對象不會爲null，但是它可能是空（empty），這時候需要完整綁定(所以我們在方法裏只要判斷isEmpty就好，不用重複判空)。 
作者語：這方法是一個高效的方法。 我是個低效的翻譯者，我看了40+分鐘。才終於明白，重要的部分已經加粗顯示。

---

實戰:

說了這麼多話，其實用起來超級簡單： 
先看如何使用getChangePayload（）方法，又附帶了中英雙語註釋

<code class="hljs fsharp has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">    /**
     * When {@link #areItemsTheSame(int, int)} returns {@code <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> two items <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span>
     * {@link #areContentsTheSame(int, int)} returns <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> them, DiffUtil
     * calls this method <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> get a payload about the change.
     * 
     * 當{@link #areItemsTheSame(int, int)} 返回<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>，且{@link #areContentsTheSame(int, int)} 返回<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>時，DiffUtils會回調此方法，
     * 去得到這個Item（有哪些）改變的payload。
     * 
     * For example, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> you are using DiffUtil <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">with</span> {@link RecyclerView}, you can <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> the
     * particular field that changed <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> the item <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> your
     * {@link android.support.v7.widget.RecyclerView.ItemAnimator ItemAnimator} can <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">use</span> that
     * information <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> run the correct animation.
     * 
     * 例如，如果你用RecyclerView配合DiffUtils，你可以返回  這個Item改變的那些字段，
     * {@link android.support.v7.widget.RecyclerView.ItemAnimator ItemAnimator} 可以用那些信息去執行正確的動畫
     * 
     * Default implementation returns {@code <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>}.\
     * 默認的實現是返回<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>
     *
     * @param oldItemPosition The position <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> the item <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> the old list
     * @param newItemPosition The position <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> the item <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> the <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> list
     * @<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> A payload object that represents the change between the two items.
     * 返回 一個 代表着新老item的改變內容的 payload對象，
     */
    @Nullable
    @Override
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Object getChangePayload(int oldItemPosition, int newItemPosition) {
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//實現這個方法 就能成爲文藝青年中的文藝青年</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 定向刷新中的部分更新</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 效率最高</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//只是沒有了ItemChange的白光一閃動畫，（反正我也覺得不太重要）</span>
        TestBean oldBean = mOldDatas.get(oldItemPosition);
        TestBean newBean = mNewDatas.get(newItemPosition);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//這裏就不用比較核心字段了,一定相等</span>
        Bundle payload = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Bundle();
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!oldBean.getDesc().equals(newBean.getDesc())) {
            payload.putString(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"KEY_DESC"</span>, newBean.getDesc());
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (oldBean.getPic() != newBean.getPic()) {
            payload.putInt(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"KEY_PIC"</span>, newBean.getPic());
        }

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (payload.size() == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果沒有變化 就傳空</span>
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> payload;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li></ul>

簡單的說，這個方法返回一個Object類型的payload，它包含了某個item的變化了的那些內容。 
我們這裏使用Bundle保存這些變化。

在Adapter裏如下重寫三參的onBindViewHolder：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">    @Override
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onBindViewHolder</span>(DiffVH holder, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> position, List<Object> payloads) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (payloads.isEmpty()) {
            onBindViewHolder(holder, position);
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//文藝青年中的文青</span>
            Bundle payload = (Bundle) payloads.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
            TestBean bean = mDatas.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>(position);
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (String key : payload.keySet()) {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (key) {
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"KEY_DESC"</span>:
                        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//這裏可以用payload裏的數據，不過data也是新的 也可以用</span>
                        holder.tv2.setText(bean.getDesc());
                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"KEY_PIC"</span>:
                        holder.iv.setImageResource(payload.getInt(key));
                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">default</span>:
                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;
                }
            }
        }
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>

這裏傳遞過來的payloads是一個List，由註釋可知，一定不爲null，所以我們判斷是否是empty， 
如果是empty，就調用兩參的函數，進行一次Full Bind。 
如果不是empty，就進行partial bind， 
通過下標0取出我們在getChangePayload方法裏返回的payload，然後遍歷payload的key，根據key檢索，如果payload裏攜帶有相應的改變，就取出來 然後更新在ItemView上。 
（這裏，通過mDatas獲得的也是最新數據源的數據，所以用payload的數據或者新數據的數據 進行更新都可以） 
至此，我們已經掌握了刷新RecyclerView，文藝青年中最文藝的那種寫法。

---

四 在子線程中使用DiffUtil

在DiffUtil的源碼頭部註釋中介紹了DiffUtil的相關信息， 
DiffUtil內部採用的Eugene W. Myers’s difference 算法，但該算法不能檢測移動的item，所以Google在其基礎上改進支持檢測移動項目，但是檢測移動項目，會更耗性能。 
在有1000項數據，200處改動時，這個算法的耗時： 
打開了移動檢測時：平均值：27.07ms，中位數：26.92ms。 
關閉了移動檢測時：平均值：13.54ms，中位數：13.36ms。 
有興趣可以自行去源碼頭部閱讀註釋，對我們比較有用的是其中一段提到， 
如果我們的list過大，這個計算出DiffResult的時間還是蠻久的，所以我們應該將獲取DiffResult的過程放到子線程中，並在主線程中更新RecyclerView。 
這裏我採用Handler配合DiffUtil使用： 
代碼如下：

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> H_CODE_UPDATE = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<TestBean> mNewDatas;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//增加一個變量暫存newList</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Handler mHandler = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Handler() {
        <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">handleMessage</span>(Message msg) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (msg.what) {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> H_CODE_UPDATE:
                    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//取出Result</span>
                    DiffUtil.DiffResult diffResult = (DiffUtil.DiffResult) msg.obj;
                    diffResult.dispatchUpdatesTo(mAdapter);
                    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//別忘了將新數據給Adapter</span>
                    mDatas = mNewDatas;
                    mAdapter.setDatas(mDatas);
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;
            }
        }
    };</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {
                <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//放在子線程中計算DiffResult</span>
                    DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DiffCallBack(mDatas, mNewDatas), <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);
                    Message message = mHandler.obtainMessage(H_CODE_UPDATE);
                    message.obj = diffResult;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//obj存放DiffResult</span>
                    message.sendToTarget();
                }
            }).start();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><div class="save_code tracking-ad" data-mod="popu_249" style="box-sizing: border-box; position: absolute; height: 60px; right: 30px; top: 5px; color: rgb(255, 255, 255); cursor: pointer; z-index: 2;"><a target=_blank target="_blank" style="color: rgb(51, 102, 153); box-sizing: border-box;"><img src="http://static.blog.csdn.net/images/save_snippets.png" style="border: none; box-sizing: border-box; max-width: 100%;" alt="" /></a></div><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

就是簡單的Handler使用，不再贅述。

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