Android ListView之EfficientAdapte的使用详解

<?xml version="1.0" encoding="utf-8"?>  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"      android:orientation="vertical"      android:layout_width="match_parent"      android:layout_height="match_parent"      android:paddingLeft="8dp"      android:paddingRight="8dp">     <ListView android:id="@id/android:list"         android:layout_width="match_parent"         android:layout_height="match_parent"         android:background="#00FF00"         android:layout_weight="1"         android:drawSelectorOnTop="false"/>     <TextView android:id="@id/android:empty"         android:layout_width="match_parent"         android:layout_height="match_parent"         android:background="#FF0000"         android:text="No data"/>  </LinearLayout> 

/**  * Demonstrates how to write an efficient list adapter. The adapter used in this example binds  * to an ImageView and to a TextView for each row in the list.  *  * To work efficiently the adapter implemented here uses two techniques:  * - It reuses the convertView passed to getView() to avoid inflating View when it is not necessary  * - It uses the ViewHolder pattern to avoid calling findViewById() when it is not necessary  *  * The ViewHolder pattern consists in storing a data structure in the tag of the view returned by  * getView(). This data structures contains references to the views we want to bind data to, thus  * avoiding calls to findViewById() every time getView() is invoked.  */ public class List14 extends ListActivity {    private static class EfficientAdapter extends BaseAdapter {     private LayoutInflater mInflater;     private Bitmap mIcon1;     private Bitmap mIcon2;      public EfficientAdapter(Context context) {       // Cache the LayoutInflate to avoid asking for a new one each time.       mInflater = LayoutInflater.from(context);        // Icons bound to the rows.       mIcon1 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_1);       mIcon2 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_2);     }      /**      * The number of items in the list is determined by the number of speeches      * in our array.      *      * @see android.widget.ListAdapter#getCount()      */     public int getCount() {       return DATA.length;     }      /**      * Since the data comes from an array, just returning the index is      * sufficent to get at the data. If we were using a more complex data      * structure, we would return whatever object represents one row in the      * list.      *      * @see android.widget.ListAdapter#getItem(int)      */     public Object getItem(int position) {       return position;     }      /**      * Use the array index as a unique id.      *      * @see android.widget.ListAdapter#getItemId(int)      */     public long getItemId(int position) {       return position;     }      /**      * Make a view to hold each row.      *      * @see android.widget.ListAdapter#getView(int, android.view.View,      *   android.view.ViewGroup)      */     public View getView(int position, View convertView, ViewGroup parent) {       // A ViewHolder keeps references to children views to avoid unneccessary calls       // to findViewById() on each row.       ViewHolder holder;        // When convertView is not null, we can reuse it directly, there is no need       // to reinflate it. We only inflate a new View when the convertView supplied       // by ListView is null.       if (convertView == null) {         convertView = mInflater.inflate(R.layout.list_item_icon_text, null);          // Creates a ViewHolder and store references to the two children views         // we want to bind data to.         holder = new ViewHolder();         holder.text = (TextView) convertView.findViewById(R.id.text);         holder.icon = (ImageView) convertView.findViewById(R.id.icon);          convertView.setTag(holder);       } else {         // Get the ViewHolder back to get fast access to the TextView         // and the ImageView.         holder = (ViewHolder) convertView.getTag();       }        // Bind the data efficiently with the holder.       holder.text.setText(DATA[position]);       holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);        return convertView;     }      static class ViewHolder {       TextView text;       ImageView icon;     }   }    @Override   public void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setListAdapter(new EfficientAdapter(this));   }    private static final String[] DATA = {       "Abbaye de Belloc", "Abbaye du Mont des Cats", "Abertam"}; }