docs/html/sdk/compatibility-library.jd

page.title=Compatibility Library

@jd:body

<div id="qv-wrapper">
<div id="qv">
  
<h2>In this document</h2>
<ol>
  <li><a href="#Notes">Revisions</a></li>
  <li><a href="#Installing">Installing the Compatibility Library</a></li>
  <li><a href="#SettingUp">Setting Up a Project to Use the Library</a></li>
  <li><a href="#Using">Using Some of the Library APIs</a></li>
  <li><a href="#Samples">Samples</a></li>
</ol>

<h2>See also</h2>
<ol>
  <li><a
href="{@docRoot}guide/practices/optimizing-for-3.0.html">Optimizing Apps for Android 3.0</a></li>
  <li><a href="http://code.google.com/p/iosched/">Google I/O App source code</a></li>
</ol>

</div>
</div>

<p><em>Minimum API level supported:</em> <b>4</b></p>

<p>The Compatibility Library is a static library you can add to your Android application in order to
use APIs not available in older versions of the Android platform. The primary goal of the library is
to provide APIs introduced in Andriod 3.0 for older versions of Android so that all applications can
use them.</p>

<p>If you're not able to use APIs introduced in Android 3.0 directly, because you want to remain
backward-compatible, the Compatibility Library provides your application access to self-contained
versions of some of the latest APIs that you can use with older versions of Android. Most
importantly, the library provides implementations of the {@link android.app.Fragment} and {@link
android.content.Loader} APIs, so you can use them in a way that's compatible with devices running
Android 1.6 (API level 4) and higher. Thus, you can more easily create a single APK that supports a
majority of devices and provide larger devices (such as tablets) a fully optimized experience by
using <a href="{@docRoot}guide/topics/fundamentals/fragments.html">Fragments</a> in your activity
design.</p>


<h2 id="Notes">Revisions</h2>

<p>The sections below provide notes about successive releases of
the Compatibility Library, as denoted by revision number.</p>


<div class="toggle-content open">

  <p><a href="#" onclick="return toggleContent(this)">
    <img src="{@docRoot}assets/images/triangle-opened.png" class="toggle-content-img" />
    Compatibility Library, revision 2 (May 2011)
  </a></p>

  <div class="toggle-content-toggleme" style="padding-left:2em"> 
    <dl>
    <dt>Changes:</dt>
    <dd>
      <ul>
        <li>Support for fragment animations.</li>
        <li>Fix {@code Fragment.onActivityResult()} bug.</li>
      </ul>
    </dd>
    </dl>
  </div>

</div>


<div class="toggle-content closed">

  <p><a href="#" onclick="return toggleContent(this)">
    <img src="{@docRoot}assets/images/triangle-closed.png" class="toggle-content-img" />
    Compatibility Library, revision 1 (March 2011)
  </a></p>

  <div class="toggle-content-toggleme" style="padding-left:2em"> 
      <p>Initial release of the library.</p>
  </div>

</div>



<h2 id="Installing">Installing the Compatibility Library</h2>

<p>The Compatibility Library is provided as a downloadable package from the Android SDK and AVD
Manager. To install the library:</p>

<ol>
  <li>Launch the SDK and AVD Manager. 
    <p>From Eclipse, you can select <strong>Window</strong>
&gt; <strong>Android SDK and AVD Manager</strong>. Or, launch {@code SDK Manager.exe} from
the {@code &lt;sdk&gt;/} directory (on Windows only) or {@code android} from the {@code
&lt;sdk&gt;/tools/} directory.</p></li>
  <li>Expand the Android Repository, check <strong>Android Compatibility package</strong>
and click <strong>Install selected</strong>.</li>
  <li>Proceed to install the package.</li>
</ol>

<p>When done, all files (including source code, samples, and the {@code .jar} file) are saved
into the <code>&lt;sdk&gt;/extras/android/compatibility/</code> directory. The next directory
name is {@code v4}, which indicates the lowest compatible version for the library within. That
is, the code in {@code v4/} supports API level 4 and above. (There may be future libraries that
have a different minimum version, so they will be saved alongside this one.)</p>


<h2 id="SettingUp">Setting Up a Project to Use the Library</h2>

<p>To add the Compatibility Library to your Android project:</p>
<ol>
  <li>In your Android project, create a directory named {@code libs} at the root of your
project (next to {@code src/}, {@code res/}, etc.)</li>
  <li>Navigate to {@code &lt;sdk&gt;/extras/android/compatibility/v4/}.</li>
  <li>Copy the {@code android-support-v4.jar} file into your project {@code libs/} directory.</li>
  <li>Add the JAR to your project build path. In Eclipse, right-click the JAR file in the
Package Explorer, select <strong>Build Path</strong> &gt; <strong>Add to Build Path</strong>.
You should then see the JAR file appear in a new directory called Referenced Libraries.</li>
</ol>

<p>Your application is now ready to use fragments, loaders and other APIs from the library. All the
provided APIs are in the {@code android.support.v4} package.</p>

<p class="warning"><strong>Warning:</strong> Be certain that you not confuse the standard
{@code android} packages with those in {@code android.support.v4}. Some code completion tools might
get this wrong, especially if you're building against recent versions of the platform. To be safe,
keep your build target set to the same version as you have defined for your <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code android:minSdkVersion}</a>
and double check the import statements for classes that are duplicated in the Compatibility
Library, such as {@code SimpleCursorAdapter}.</p>


<h2 id="Using">Using Some of the Library APIs</h2>

<p>The Compatibility Library provides access to several classes introduced with Android 3.0, plus
some updated version of existing classes. Some of the most useful and notable classes in the
library are:</p>

<ul>
  <li>{@link android.app.Fragment}</li>
  <li>{@link android.app.FragmentManager}</li>
  <li>{@link android.app.FragmentTransaction}</li>
  <li>{@link android.app.ListFragment}</li>
  <li>{@link android.app.DialogFragment}</li>
  <li>{@link android.app.LoaderManager}</li>
  <li>{@link android.content.Loader}</li>
  <li>{@link android.content.AsyncTaskLoader}</li>
  <li>{@link android.content.CursorLoader}</li>
</ul>

<p>For each of the classes above (and others not listed), the APIs work almost exactly the same
as the counterparts in the latest version of the Android platform. Thus, you can usually refer to
the latest reference documentation for information about the supported APIs. There are some
differences, however. Most notably:</p>

<ul>
  <li>When creating an activity to use fragments, you must declare your activity to extend the
{@code FragmentActivity} class (instead of the traditional {@link android.app.Activity}
class).</li>
  <li>To manage your fragments and loaders, you must use the methods {@code
FragmentActivity.getSupportFragmentManager()} and {@code
FragmentActivity.getSupportLoaderManager()} (instead of the {@link
android.app.Activity#getFragmentManager()} and {@link android.app.Activity#getLoaderManager()}
methods).</li>
  <li>The {@link android.app.ActionBar} is <strong>not supported</strong> by the library.
However, when creating your <a href="{@docRoot}guide/topics/ui/menus.html#options-menu">Options
Menu</a>, you can declare which items should be added to the Action Bar when it's available (on
Android 3.0 or later). You can do so with the {@code MenuCompat.setShowAsAction()} method. For
example:
<pre>
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.options, menu);
    MenuCompat.setShowAsAction(menu.findItem(R.id.action_search), 1);
    return true;
}
</pre>
</li>
</ul>

<p>The Compatibility Library currently does not provide reference documentation for the included
APIs. To generate your own set, using the {@code javadoc} tool, perform the
following from a command line:</p>

<pre class="no-pretty-print">
cd &lt;sdk&gt;/extras/android/compatibility/v4/
mkdir docs
javadoc -sourcepath src/java/ -subpackages android.support.v4 -d docs
</pre>
<p>Open the {@code docs/index.html} file to begin browsing the generated documentation.</p>


<div class="note"><p><strong>Tip:</strong> To enable the Holographic theme on devices
running Android 3.0 or higher, declare in your manifest file that your application targets
API level 11. For example:</p>
<pre>
&lt;uses-sdk android:minSdkVersion="4" android:targetSdkVersion="11" /&gt;
</pre>
<p>This way, your application automatically receives the Holographic theme and the Action Bar for 
each activity when running on Android 3.0 and higher.</p>
</div>

<p>For more information about how you can optimize your application for the latest
Android-powered devices, read <a href="{@docRoot}guide/practices/optimizing-for-3.0.html">Optimizing
Apps for Android 3.0</a>.</p>


<h2 id="Samples">Samples</h2>

<p>If you want to see some sample code that uses the Compatibility Library, take a look at the
<a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/support/index.html">API
Demos</a> sample code that's included with the Samples package you can download from the AVD and SDK
Manager.</p>

<p>Additionally, the <a href="http://code.google.com/p/iosched/">Google I/O App</a> is a complete
application that uses the library to provide a single APK for both handsets and tablets and also
demonstrates some of Android's best practices in Android UI design.</p>