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"}; 
}