Android適配器

一：適配器中提高性能優化如下：

1.利用convertView

利用Android的Recycler機制，利用convertView來重新回收View，效率有了本質提高。View的每次創建是比較耗時的，因此對於getview方法傳入的convertView應充分利用 != null的判斷 。

2.使用ViewHolder

ViewHolder將需要緩存的view封裝好，convertView的setTag纔是將這些緩存起來供下次調用。 當你的listview里布局多樣化的時候 viewholder的作用體現明顯，效率再一次提高。 View的findViewById()方法也是比較耗時的，因此需要考慮只調用一次，之後就用View.getTag()方法來獲得ViewHolder對象。

3.優雅的使用ViewHolder

使用ViewHolder時，每次一遍一遍的findViewById，一遍一遍在ViewHolder裏面添加View的定義，view一多，是不是感覺煩爆了，base-adapter-helper這個類庫似乎完美的解決了這個問題。

萬能適配器參考：http://www.2cto.com/kf/201507/414816.html

二、單獨更新某一個item的數據

使listview和gridview更新數據常用的是notifyDataSetChanged，可以更新適配器的數據，但是這種方式是數據全部更新，適配數據的時候會出現閃爍的現象，但是有的時候只是想更新某一條或某部分數據，這裏可以單獨寫一個更新數據的方法，達到只更新指定的一條item。
下面是我寫的一個gridview隨機更換圖片的demo。listview請參考
：http://blog.csdn.net/jdsjlzx/article/details/45582719

(1)適配器類：

public class PictureAdapter extends BaseAdapter {
    private Context mContext;
    private List<PictureData> mPictures;
    private GridView mGridView;
    public PictureAdapter(Context context, List<PictureData> pictures) {
        this.mContext = context;
        this.mPictures = pictures;
    }
    public void setPictureDatas(List<PictureData> pictures){
        this.mPictures = pictures;
    }
    /**
     * 設置gridview對象
     * @param gridV
     */
    public void setGridView(GridView gridV) {
        this.mGridView = gridV;
    }
    /**
     * update listview 單條數據
     * 
     * @param item
     *            新數據對象
     */
    public void updateItemData(PictureData picture) {
        Message msg = Message.obtain();
        int ids = -1;
        // 進行數據對比獲取對應數據在list中的位置
        for (int i = 0; i < mPictures.size(); i++) {
            if (mPictures.get(i).getId() == picture.getId()) {
                ids = i;
            }
        }
        msg.arg1 = ids;
        // 更新mDataList對應位置的數據
        mPictures.set(ids, picture);
        // handle刷新界面
        han.sendMessage(msg);
    }
    @SuppressLint("HandlerLeak")
    private Handler han = new Handler() {
        public void handleMessage(android.os.Message msg) {
            updateItem(msg.arg1);
        };
    };
    /**
     * 刷新指定item
     * 
     * @param index
     * item在gridview中的位置
     */
    private void updateItem(int index) {
        if (mGridView == null) {
            return;
        }
        View convertView = mGridView.getChildAt(index);
        // 重新設置界面顯示數據
        Holder holder = new Holder();
        holder.img_picture = (ImageView) convertView.findViewById(R.id.img_picture);
        holder.tv_picture_name = (TextView) convertView.findViewById(R.id.tv_picture_name);
        holder.setView(index);
    }
    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return mPictures.size();
    }
    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return mPictures.get(position);
    }
    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Holder holder;
        if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(
                    R.layout.adapter_picture_item_layout, null);
            holder = new Holder();
            holder.tv_picture_name = (TextView) convertView
                    .findViewById(R.id.tv_picture_name);
            holder.img_picture = (ImageView) convertView
                    .findViewById(R.id.img_picture);
            convertView.setTag(holder);
        } else {
            holder = (Holder) convertView.getTag();
        }
        holder.setView(position);
        return convertView;
    }
    /**
     * listview 和gridview的緩存。
     * @author Administrator
     *
     */
    class Holder {
        TextView tv_picture_name;
        ImageView img_picture;
        public void setView(int position) {
            PictureData picture = mPictures.get(position);
            try {
                String name = picture.getName();
                int resoure = picture.getResoure();
                //tv_picture_name.setText(name);
                img_picture.setImageResource(resoure);
                Log.i("tag", "resoure:"+resoure);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

(2).Activity類的實現：

public class PictureActivity extends Activity implements OnClickListener {
    Button bt_type;
    Button bt_change;
    ListView lv_picture;
    GridView gv_picture;
    private static final int TYPE_LIST = 1;
    private static final int TYPE_GRID = TYPE_LIST + 1;
    private static final int MSG_CHANGE_PICTURE = 10000;
    private int type = TYPE_GRID; // 1:listview;2:gridview
    private int[] pictuereDrawables = { R.drawable.header01,
            R.drawable.header02, R.drawable.header03, R.drawable.header04,
            R.drawable.header05, R.drawable.header06, R.drawable.header07,
            R.drawable.header08, R.drawable.header09, R.drawable.header10,
            R.drawable.header11, R.drawable.header12, R.drawable.header13,
            R.drawable.header14, R.drawable.header15, R.drawable.header16,
            R.drawable.header17, R.drawable.header18, R.drawable.header19,
            R.drawable.header20, R.drawable.header21, R.drawable.header22,
            R.drawable.header23 };
    private List<PictureData> pictures;
    private PictureAdapter mPictureAdapter;
    private boolean isChanging = false;
    UpdatePictureThread pictureThread;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_adpater);
        initView();
        getPictureData();
        mPictureAdapter = new PictureAdapter(this, pictures);
        mPictureAdapter.setGridView(gv_picture);
        // lv_picture.setAdapter(mPictureAdapter);
        gv_picture.setAdapter(mPictureAdapter);
    }
    private void initView() {
        bt_type = (Button) findViewById(R.id.bt_type);
        bt_change = (Button) findViewById(R.id.bt_change);
        lv_picture = (ListView) findViewById(R.id.lv_picture);
        gv_picture = (GridView) findViewById(R.id.gv_picture);
        bt_type.setOnClickListener(this);
        bt_change.setOnClickListener(this);
        showTypeView();
    }
    private void showTypeView() {
        switch (type) {
        case TYPE_LIST:
            lv_picture.setVisibility(View.VISIBLE);
            gv_picture.setVisibility(View.GONE);
            break;
        case TYPE_GRID:
            lv_picture.setVisibility(View.GONE);
            gv_picture.setVisibility(View.VISIBLE);
            break;
        default:
            break;
        }
    }
    @Override
    public void onClick(View v) {
        switch (v.getId()) {
        case R.id.bt_type:
            if (type == TYPE_LIST) {
                type = TYPE_GRID;
            } else {
                type = TYPE_LIST;
            }
            showTypeView();
            break;
        case R.id.bt_change:
            if (isChanging) {
                stopThread();
            } else {
                if (pictureThread == null) {
                    pictureThread = new UpdatePictureThread();
                }
                pictureThread.start();
                isChanging = true;
            }
            break;
        default:
            break;
        }
    }
    private void getPictureData() {
        pictures = new ArrayList<PictureData>();
        for (int i = 0; i < pictuereDrawables.length; i++) {
            PictureData picture = new PictureData();
            picture.setId(1 + i);
            picture.setName("person_" + (int) (i + 1));
            picture.setResoure(pictuereDrawables[i]);
            pictures.add(picture);
        }
    }
    class UpdatePictureThread extends Thread {
        @Override
        public void run() {
            // TODO Auto-generated method stub
            super.run();
            while (isChanging) {
                try {
                    sleep(100);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                handler.sendEmptyMessage(MSG_CHANGE_PICTURE);
            }
        }
    }
    Handler handler = new Handler() {
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case MSG_CHANGE_PICTURE:
                int length = pictuereDrawables.length;
                Random random = new Random();
                int changeIndex = random.nextInt(length);
                int resoureIndex = random.nextInt(length);
                if (changeIndex != resoureIndex) {
                    pictures.get(changeIndex).setResoure(
                            pictuereDrawables[resoureIndex]);
                    mPictureAdapter.setPictureDatas(pictures);
                    mPictureAdapter.updateItemData(pictures.get(changeIndex));
                }
                break;
            default:
                break;
            }
        };
    };
    private void stopThread() {
        if (pictureThread != null) {
            if (pictureThread.isAlive()) {
                pictureThread.interrupt();
                pictureThread = null;
            }
        }
        isChanging = false;
    }
}

(3)數據類的實現如下：

public class PictureData {
    private int id;
    private String name;
    private int resoure;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getResoure() {
        return resoure;
    }
    public void setResoure(int resoure) {
        this.resoure = resoure;
    }
}

(4).adapter_picture_item_layout 的實現如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
     >
    <ImageView android:id="@+id/img_picture"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_centerInParent="true"
        android:src="@drawable/header01"/>

    <TextView android:id="@+id/tv_picture_name"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="picture_1"
        android:layout_margin="5dp"
        android:padding="5dp"
        android:visibility="gone"
        android:layout_alignParentBottom="true"/>
</RelativeLayout>  

(5).activity_picture類的實現如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >
        <Button
            android:id="@+id/bt_type"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="change" />

        <Button
            android:id="@+id/bt_change"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="start" />


    </LinearLayout>
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_marginTop="10dp"
        android:orientation="vertical" >
        <ListView
            android:id="@+id/lv_picture"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
        </ListView>
        <GridView
            android:id="@+id/gv_picture"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:numColumns="4"
            android:visibility="gone" >
        </GridView>
    </LinearLayout>
</LinearLayout>  

三：適配器中注意事項：

1、適配器中如果添加頂部或者底部的view的時候。
setOnItemClickListener方法需要注意，可能導致添加的view佔位，listview調用setOnItemClickListener的時候出現錯位現象。解決這個問題可以使用回調的方式，在itemView中實現點擊事件，並把響應返回給listview。
2、適配器中item如果有顯示和隱藏處理
即setVisible,做出判斷的時候，一定要指明是隱藏還是顯示，否則或出現listview滾動的時候隱藏顯示的view混亂的現象。

本文摘抄一下網站，內容更豐富，詳細可閱讀原文：
http://www.2cto.com/kf/201507/414816.html
http://blog.csdn.net/jdsjlzx/article/details/45582719