/**
* 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",
"Abondance", "Ackawi", "Acorn", "Adelost", "Affidelice au Chablis",
"Afuega'l Pitu", "Airag", "Airedale", "Aisy Cendre", ...
2009/1/31 skink <[email protected]>:
>
> hi,
>
> i want to create custom View showing possibly several items.
>
> i think using Adapter interface would be good idea.
>
> my question is: should i extend AdapterView? if so, what is the most
> imortant when doing this (e.g. AdapterView is ViewGroup, so how should
> i manage children)?
>
> thanks,
> pskink
>
> >
>
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