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"}; 
}