Android布局---List View
本文译自：http://developer.android.com/guide/topics/ui/layout/listview.html
ListView是一个用于显示可滚动的项目列表的View组。它适应一个Adapter来自动的插入列表项，该Adapter会从诸如数组或数据库查询中拉入内容，并把每个项目结果转换成一个可放入列表的View。
对于如何使用adapter来自动的插入View的介绍，请看使用Adapter来创建布局。
使用装载器
为了避免查询时阻塞你的应用程序的主线程，使用CursorLoader异步任务来查询Cursor是一种标准的方法。当CursorLoader接收到Cursor结果时，LoaderCallbacks会收到一个对onLoadFinished()方法的回调，这是你用新的Cursor来更新你的Adapter的地方，然后列表View显示结果。
尽管CursorLoader API在Android3.0（API Level 11）中被首次引入，但是这些API在支持类库中也是有效的，因此在支持运行Android1.6以上的设备中，你的应用程序也可以使用。
有关使用Loader来异步加载数据的信息，请看Loaders指南。
示例
下面的示例使用了ListActivity，默认情况下，它是一个只包含一个ListView布局元素的Activity。它执行对Contacts Provider查询，来获得姓名和电话号码列表。
为了使用CursorLoader来给列表View自动的加载数据，这个Activity实现了LoaderCallbacks接口。
public class ListViewLoader extends ListActivity
implements LoaderManager.LoaderCallbacks<Cursor> {
// This is the Adapter being used to display the list's data
SimpleCursorAdapter mAdapter;
// These are the Contacts rows that we will retrieve
static final String[] PROJECTION = new String[] {ContactsContract.Data._ID,
ContactsContract.Data.DISPLAY_NAME};
// This is the select criteria
static final String SELECTION = "((" +
ContactsContract.Data.DISPLAY_NAME + " NOTNULL) AND (" +
ContactsContract.Data.DISPLAY_NAME + " != '' ))";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Create a progress bar to display while the list loads
ProgressBar progressBar = new ProgressBar(this);
progressBar.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
LayoutParams.WRAP_CONTENT, Gravity.CENTER));
progressBar.setIndeterminate(true);
getListView().setEmptyView(progressBar);
// Must add the progress bar to the root of the layout
ViewGroup root = (ViewGroup) findViewById(android.R.id.content);
root.addView(progressBar);
// For the cursor adapter, specify which columns go into which views
String[] fromColumns = {ContactsContract.Data.DISPLAY_NAME};
int[] toViews = {android.R.id.text1}; // The TextView in simple_list_item_1
// Create an empty adapter we will use to display the loaded data.
// We pass null for the cursor, then update it in onLoadFinished()
mAdapter = new SimpleCursorAdapter(this,
android.R.layout.simple_list_item_1, null,
fromColumns, toViews, 0);
setListAdapter(mAdapter);
// Prepare the loader. Either re-connect with an existing one,
// or start a new one.
getLoaderManager().initLoader(0, null, this);
}
// Called when a new Loader needs to be created
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// Now create and return a CursorLoader that will take care of
// creating a Cursor for the data being displayed.
return new CursorLoader(this, ContactsContract.Data.CONTENT_URI,
PROJECTION, SELECTION, null, null);
}
// Called when a previously created loader has finished loading
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// Swap the new cursor in. (The framework will take care of closing the
// old cursor once we return.)
mAdapter.swapCursor(data);
}
// Called when a previously created loader is reset, making the data unavailable
public void onLoaderReset(Loader<Cursor> loader) {
// This is called when the last Cursor provided to onLoadFinished()
// above is about to be closed. We need to make sure we are no
// longer using it.
mAdapter.swapCursor(null);
}
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Do something when a list item is clicked
}
}
注意：因为这个例子要执行对Contacts Provider的查询，所以如果想要执行这段代码，你的应用程序需要在清单文件中申请READ_CONTACTS权限：
<uses-permission android:name="android.permission.READ_CONTACTS" />