docs/html/training/load-data-background/setup-loader.jd

page.title=Setting Up the Loader
trainingnavtop=true
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@jd:body

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<h2>This lesson teaches you to</h2>
<ol>
    <li>
        <a href="#AddExtensions">Extend an Activity</a>
    </li>
    <li>
        <a href="#GetLoader">Retrieve a LoaderManager</a>
    </li>
    <li>
        <a href="#InitializeLoader">Initialize the Loader Framework</a>
    </li>
</ol>
  </div>
</div>
<p>
    You create a {@link android.support.v4.content.CursorLoader} within a
    <b>loader framework</b>. To set up the framework, you implement the
    {@link android.support.v4.app.LoaderManager.LoaderCallbacks LoaderCallbacks&lt;Cursor&gt;}
    as part of an {@link android.app.Activity}. In addition, to provide compatibility
    compatible with platform versions starting with Android 1.6, you must extend the
    {@link android.app.Activity} with the {@link android.support.v4.app.FragmentActivity} class.
</p>
<p class="note">
    <strong>Note:</strong> A {@link android.support.v4.app.Fragment} is not a prerequisite for
    {@link android.support.v4.content.CursorLoader}. As a convenience, the support library class
    {@link android.support.v4.app.FragmentActivity} contains the fragment and the loader frameworks,
    but they are completely independent of each other.
</p>
<p>
    Before you can use the loader framework, you need to initialize it. To do this, retrieve
    a {@link android.support.v4.app.LoaderManager} object and call its
    {@link android.support.v4.app.LoaderManager#initLoader initLoader()} method.
</p>
<p>
    If you do use one or more {@link android.support.v4.app.Fragment} objects in an
    {@link android.app.Activity}, the {@link android.support.v4.app.LoaderManager} you retrieve is
    available to all of them.
</p>
<h2 id="AddExtensions">Extend an Activity</h2>
<p>
    To set up an {@link android.app.Activity} subclass to contain a
    {@link android.support.v4.content.CursorLoader}, extend the subclass with
    must extend {@link android.support.v4.app.FragmentActivity}, which provides the loader
    framework, and implement the {@link android.support.v4.app.LoaderManager.LoaderCallbacks
    LoaderCallbacks&lt;Cursor&gt;} interface, which specifies method signatures that the loader
    framework uses to interact with the {@link android.app.Activity}.
</p>
<p>
    For example:
</p>
<pre>
public class DisplayActivity extends FragmentActivity
        implements LoaderManager.LoaderCallbacks&lt;Cursor&gt;
</pre>
<h2 id="GetLoader">Retrieve a LoaderManager</h2>
<p>
    To get an instance {@link android.support.v4.app.LoaderManager} for use in your
    {@link android.app.Activity}, call
    {@link android.support.v4.app.FragmentActivity#getSupportLoaderManager
    FragmentActivity.getSupportLoaderManager()} at the beginning of the
    {@link android.app.Activity#onCreate onCreate()} method. For example:
</p>
<pre>
private LoaderManager mLoaderManager;
public void onCreate() {
...
mLoaderManager = this.getSupportLoaderManager();
</pre>
<h2 id="InitializeLoader">Initialize the Loader Framework</h2>
<p>
    Once you have the {@link android.support.v4.app.LoaderManager} object, initialize
    it by calling {@link android.support.v4.app.LoaderManager#initLoader initLoader()}. For
    example:
</p>
<pre>
// CursorLoader instance identifier
public static final int URL_LOADER = 0;
...
// Initializes the CursorLoader
getSupportLoaderManager().initLoader(URL_LOADER, null, this);
</pre>