安卓---API GUIDES---List View
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ListView是一个ViewGroup,用来显示滑动项的列表。使用一个适配器把列表项被自动的增加到列表。从一个资源如队列或数据库中查询内容,获取每个项的结果,放到在列表中显示的视图项中。
为了介绍如何使你能够动态的使用一个适配器加入视图,读Building Layouts with an Adapter。
http://developer.android.com/guide/topics/ui/declaring-layout.html#AdapterViews
一 使用一个加载器
使用一个CursorLoader,它是一个标准方式去查询一个Cursor,就像一个同步进程为了避免死锁你的应用程序的主线程。当这个CursorLoader接收到Cursor结果,这个LoaderCallbacks接收一个回调去onLoadFinished(),在这里你使用这个新的Cursor更新你的Adapter和列表视图,当显示结果的时候。
虽然CursorLoaderAIP在安卓3.0里第一介绍,他们同样被包含在Suport Library中,所有你可以在你的APP中使用他们以支持运行在安卓1.6以上的设备上。
二 实例
下面的实例中使用ListActivity,这个活动包含一个ListView。它执行一个查询到Contacts Provider获取一个名字和电话号码的列表。
这个活动实现这个LoaderCallbacks接口,为了使用一个CursorLoader,它动态加载数据到列表视图。
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 }}
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