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page.title=List View
page.tags=listview
@jd:body
<div id="qv-wrapper">
<div id="qv">
<h2>In this document</h2>
<ol>
<li><a href="#Loader">Using a Loader</a></li>
<li><a href="#Example">Example</a></li>
</ol>
<h2>Key classes</h2>
<ol>
<li>{@link android.widget.ListView}</li>
<li>{@link android.widget.Adapter}</li>
<li>{@link android.support.v4.content.CursorLoader}</li>
</ol>
<h2>See also</h2>
<ol>
<li><a
href="{@docRoot}guide/components/loaders.html">Loaders</a></li>
</ol>
</div>
</div>
<p>{@link android.widget.ListView} is a view group that displays a list of
scrollable items. The list items are automatically inserted to the list using an {@link
android.widget.Adapter} that pulls content from a source such as an array or database query and
converts each item result into a view that's placed into the list.</p>
<p>For an introduction to how you can dynamically insert views using an adapter, read
<a href="{@docRoot}guide/topics/ui/declaring-layout.html#AdapterViews">Building Layouts with
an Adapter</a>.</p>
<img src="{@docRoot}images/ui/listview.png" alt="" />
<h2 id="Loader">Using a Loader</h2>
<p>Using a {@link
android.support.v4.content.CursorLoader} is the standard way to query a {@link
android.database.Cursor} as an asynchronous task in order to avoid blocking your app's main thread
with the query. When the {@link android.support.v4.content.CursorLoader} receives the {@link
android.database.Cursor} result, the {@link android.support.v4.app.LoaderManager.LoaderCallbacks
LoaderCallbacks} receives a callback to {@link
android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()}, which is
where you update your {@link
android.widget.Adapter} with the new {@link android.database.Cursor} and the list view then
displays the results.</p>
<p>Although the {@link android.support.v4.content.CursorLoader} APIs were first introduced in
Android 3.0 (API level 11), they are also available in the <a
href="{@docRoot}tools/support-library/index.html">Support Library</a> so that your app may use them
while supporting devices running Android 1.6 or higher.</p>
<p>For more information about using a {@link
android.support.v4.content.Loader} to asynchronously load data, see the <a
href="{@docRoot}guide/components/loaders.html">Loaders</a> guide.</p>
<h2 id="Example">Example</h2>
<p>The following example uses {@link android.app.ListActivity}, which is an activity that includes
a {@link android.widget.ListView} as its only layout element by default. It performs a query to
the <a
href="{@docRoot}guide/topics/providers/contacts-provider.html">Contacts
Provider</a> for a list of names and phone numbers.</p>
<p>The activity implements the {@link android.support.v4.app.LoaderManager.LoaderCallbacks
LoaderCallbacks} interface in order to use a {@link android.support.v4.content.CursorLoader} that
dynamically loads the data for the list view.</p>
<pre>
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
}
}
</pre>
<p class="note"><strong>Note:</strong> Because this sample performs a query on the <a
href="{@docRoot}guide/topics/providers/contacts-provider.html">Contacts
Provider</a>, if you want to
try this code, your app must request the {@link android.Manifest.permission#READ_CONTACTS}
permission in the manifest file:<br/>
<code><uses-permission android:name="android.permission.READ_CONTACTS" /></code></p>
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