在新版本的android系統中RecyclerView作爲ListView的優化版本,封裝了ViewHolder,這樣就可以更加方便的使用這個控件。但是相比較ListView,RecyclerView沒有提供相應的addHeaderView和addFooterView方法,我們知道在一些下拉控件的實現中,都是設置了headerView或者是footerView,然後不斷的設置padding來實現的。那既然RecyclerView沒有addHeaderView和addFooterView這些方法,那麼是不是就不能實現下拉刷新這樣的功能了呢?當然不是。下面就帶大家實現一個簡易的實現addHeaderView和addFooterView的方法。
我們知道像需要適配器的這些控件,它們的數據都是通過Adapter的提供的。那麼我們就着手改造我們的Adapter。首先我們創建一個自定義的Adapter類繼承RecyclerView.Adapter
public class HeaderRecyclerViewAdapter extends RecyclerView.Adapter<HeaderRecyclerViewAdapter
.HeaderViewHolder> {
//header view type的開始值
private final int RECYCLER_HEADER_TYPE_BASE = 0xff11;
//footer view type的開始值
private final int RECYCLER_FOOTER_TYPE_BASE = 0xff22;
//header和footer的id值
private final int RECYCLER_HEADER_FOOTER_ID = -1;
//用來存放所有的header view的信息
private List<FixedInfo> mHeaders = new ArrayList<>();
//用來存放所有的footer view的信息
private List<FixedInfo> mFooters = new ArrayList<>();
//保存使用默認的RecyclerView.Adapter創建的adapter的值,這個值必須獲取到
private RecyclerView.Adapter mAdapter = null;
public HeaderRecyclerViewAdapter() {
}
public HeaderRecyclerViewAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
public void setAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
我們創建一個HeaderRecyclerViewAdapter類用來包裝我們原始的RecyclerView.Adapter類,mAdpter就是對這個原始類的應用。同樣創建了兩個ArrayList用來保存我們的Headers和footers,這裏面有一個FixedInfo類,這個類是幹嘛的呢?
//用來保存footer和headers的信息
private class FixedInfo {
public View view;
public int type;
}
這個類比較簡單,view保存我們設置的view,type用來保存我們view的type信息,可以通過type信息識別我們的header和footer。
public void addHeader(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_HEADER_TYPE_BASE + mHeaders.size();
mHeaders.add(info);
}
public void addFooter(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_FOOTER_TYPE_BASE + mFooters.size();
mFooters.add(info);
}
可以看到,每次addHeader或者是addFooter的時候,都通過一個唯一的type信息來區別這個view。
@Override
public long getItemId(int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adjPosition = position - headerCount;
return mAdapter.getItemId(adjPosition);
}
return RECYCLER_HEADER_FOOTER_ID;
}
我們需要重新getItemId()方法,如果是header或者是footer的話,直接返回我們定義的特殊值 RECYCLER_HEADER_FOOTER_ID。如果是adapter中的數據則返回adapter中的相同方法。
@Override
public int getItemViewType(int position) {
if (mAdapter == null) {
throw new IllegalStateException("must have a adapter");
}
int headerCount = getHeaderSize();
int adapterCount = mAdapter.getItemCount();
if (position < headerCount) {
return mHeaders.get(position).type;
} else if (position >= (headerCount + adapterCount)) {
return mFooters.get(position - headerCount - adapterCount).type;
} else {
int adjPosition = position - headerCount;
return mAdapter.getItemViewType(adjPosition);
}
}
getItemViewType()是我們必須重寫的方法,在這個方法中,我們會標識每一個Header和Footer的viewType。
@Override
public HeaderViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (isHeaderView(viewType)) {
int delta = viewType - RECYCLER_HEADER_TYPE_BASE;
View view = mHeaders.get(delta).view;
return new HeaderViewHolder(view);
}
if (isFooterView(viewType)) {
int delta = viewType - RECYCLER_FOOTER_TYPE_BASE;
View view = mFooters.get(delta).view;
return new HeaderViewHolder(view);
}
return (HeaderViewHolder) mAdapter.onCreateViewHolder(parent,viewType);
}
@Override
public void onBindViewHolder(HeaderViewHolder holder, int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adapterCount = mAdapter.getItemCount();
int adjPosition = position - headerCount;
if (adjPosition >= 0 && adjPosition < adapterCount) {
mAdapter.onBindViewHolder(holder, adjPosition);
}
}
}
最主要的地方來了,在onCreateViewHolder中,我們需要判斷當前的viewType是header的還是footer的,如果是header的或者footer的,我們需要算出這個viewtype所對應的view,用這個view來返回HeaderViewHolder。而在onBindViewHolder()方法中,我們只需要定位到屬於adapter中的數據就好,然後返回對應的方法即可。完整的代碼如下:
package com.gearmotion.app.mylibrary;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;
import java.util.ArrayList;
import java.util.List;
/**
* Created by Charles on 2016/3/21.
*/
public class HeaderRecyclerViewAdapter extends RecyclerView.Adapter<HeaderRecyclerViewAdapter
.HeaderViewHolder> {
//header view type的開始值
private final int RECYCLER_HEADER_TYPE_BASE = 0xff11;
//footer view type的開始值
private final int RECYCLER_FOOTER_TYPE_BASE = 0xff22;
//header和footer的id值
private final int RECYCLER_HEADER_FOOTER_ID = -1;
//用來存放所有的header view的信息
private List<FixedInfo> mHeaders = new ArrayList<>();
//用來存放所有的footer view的信息
private List<FixedInfo> mFooters = new ArrayList<>();
//保存使用默認的RecyclerView.Adapter創建的adapter的值,這個值必須獲取到
private RecyclerView.Adapter mAdapter = null;
public HeaderRecyclerViewAdapter() {
}
public HeaderRecyclerViewAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
public void setAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
@Override
public HeaderViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (isHeaderView(viewType)) {
int delta = viewType - RECYCLER_HEADER_TYPE_BASE;
View view = mHeaders.get(delta).view;
return new HeaderViewHolder(view);
}
if (isFooterView(viewType)) {
int delta = viewType - RECYCLER_FOOTER_TYPE_BASE;
View view = mFooters.get(delta).view;
return new HeaderViewHolder(view);
}
return (HeaderViewHolder) mAdapter.onCreateViewHolder(parent,viewType);
}
@Override
public void onBindViewHolder(HeaderViewHolder holder, int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adapterCount = mAdapter.getItemCount();
int adjPosition = position - headerCount;
if (adjPosition >= 0 && adjPosition < adapterCount) {
mAdapter.onBindViewHolder(holder, adjPosition);
}
}
}
@Override
public int getItemCount() {
if (mAdapter != null) {
return mHeaders.size() + mAdapter.getItemCount() + mFooters.size();
} else {
return mHeaders.size() + mFooters.size();
}
}
@Override
public int getItemViewType(int position) {
if (mAdapter == null) {
throw new IllegalStateException("must have a adapter");
}
int headerCount = getHeaderSize();
int adapterCount = mAdapter.getItemCount();
if (position < headerCount) {
return mHeaders.get(position).type;
} else if (position >= (headerCount + adapterCount)) {
return mFooters.get(position - headerCount - adapterCount).type;
} else {
int adjPosition = position - headerCount;
return mAdapter.getItemViewType(adjPosition);
}
}
@Override
public long getItemId(int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adjPosition = position - headerCount;
return mAdapter.getItemId(adjPosition);
}
return RECYCLER_HEADER_FOOTER_ID;
}
public void addHeader(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_HEADER_TYPE_BASE + mHeaders.size();
mHeaders.add(info);
}
public void addFooter(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_FOOTER_TYPE_BASE + mFooters.size();
mFooters.add(info);
}
public int getHeaderSize() {
return mHeaders.size();
}
public int getFooterSize() {
return mFooters.size();
}
private boolean isHeaderView(int type) {
int delta = type - RECYCLER_HEADER_TYPE_BASE;
return delta >= 0 && delta < mHeaders.size();
}
private boolean isFooterView(int type) {
int delta = type - RECYCLER_FOOTER_TYPE_BASE;
return delta >= 0 && delta < mFooters.size();
}
//用來保存footer和headers的信息
private class FixedInfo {
public View view;
public int type;
}
//自定義的viewholder
public static class HeaderViewHolder extends RecyclerView.ViewHolder {
public HeaderViewHolder(android.view.View itemView) {
super(itemView);
}
}
}
最後我們在使用的時候將原始創建的adapter傳遞給HeaderRecyclerViewAdapter即可。
package com.gearmotion.app.headerrecyclerviewmotion;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.text.Layout;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.gearmotion.app.mylibrary.HeaderRecyclerViewAdapter;
public class MainActivity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private LayoutInflater mInflater;
private String[] mDatas = new String[]{"title1", "title2", "title3", "title4", "title5",
"title6"};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mInflater = LayoutInflater.from(this);
mRecyclerView = (RecyclerView) this.findViewById(R.id.recyclerview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
CustomAdapter tmpAdapter = new CustomAdapter();
HeaderRecyclerViewAdapter mAdapter = new HeaderRecyclerViewAdapter(tmpAdapter);
mAdapter.addHeader(createView("head1"));
mAdapter.addHeader(createView("head2"));
mAdapter.addHeader(createView("head3"));
mAdapter.addFooter(createView("foot1"));
mAdapter.addFooter(createView("foot2"));
mAdapter.addFooter(createView("foot3"));
mRecyclerView.setAdapter(mAdapter);
}
private View createView(String title) {
TextView tv = new TextView(this);
tv.setText(title);
tv.setLayoutParams(new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
70));
tv.setGravity(Gravity.CENTER);
return tv;
}
public class CustomAdapter extends RecyclerView.Adapter<CustomViewHolder> {
@Override
public CustomViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View root = mInflater.inflate(R.layout.item, null);
return new CustomViewHolder(root);
}
@Override
public void onBindViewHolder(CustomViewHolder holder, int position) {
holder.textView.setText(mDatas[position]);
}
@Override
public int getItemCount() {
return mDatas.length;
}
}
public class CustomViewHolder extends HeaderRecyclerViewAdapter.HeaderViewHolder {
public TextView textView;
public CustomViewHolder(View itemView) {
super(itemView);
textView = (TextView) itemView.findViewById(R.id.itemtextview);
}
}
}
結果如下:
代碼地址如下:https://github.com/summerpxy/HeaderRecyclerViewAdapter.git