page.title=List View
parent.title=Layouts
parent.link=declaring-layout.html
@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/extras/support-library.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&lt;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 + " != '' ))";

    &#64;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&lt;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&lt;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&lt;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);
    }

    &#64;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>&lt;uses-permission android:name="android.permission.READ_CONTACTS" /></code></p>

