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" />