android_frameworks_base/docs/html/training/appbar/up-action.jd

page.title=Adding an Up Action
page.tags="appbar","actionbar", "up"
helpoutsWidget=true
trainingnavtop=true

@jd:body

<div id="tb-wrapper">
  <div id="tb">

    <h2>This lesson teaches you to</h2>

    <ol>
      <li>
        <a href="#declare-parent">Declare a Parent Activity</a>
      </li>

      <li>
        <a href="#enable-up">Enable the Up Button</a>
      </li>
    </ol>

    <h2>See Also</h2>
    <ul>
      <li><a href="{@docRoot}training/implementing-navigation/ancestral.html">
          Providing Up Navigation</a></li>
    </ul>


  </div>
</div>

<p>
  Your app should make it easy for users to find their way back to the app's
  main screen. One simple way to do this is to provide an <em>Up</em>
  button on the app bar for all activities except the main one. When the user
  selects the <em>Up</em> button, the app navigates to the parent
  activity.
</p>

<p>
  This lesson shows you how to add an <em>Up</em> button to an activity by
  declaring the activity's parent in the manifest, and enabling the app bar's
  <em>Up</em> button.
</p>

<h2 id="declare-parent">Declare a Parent Activity</h2>

<p>
  To support the up functionality in an activity, you need to declare the
  activity's parent. You can do this in the app manifest, by setting an
  <code>android:parentActivityName</code> attribute.
</p>

<p>
  The <code>android:parentActivityName</code> attribute
  was introduced in Android 4.1 (API level 16). To support devices with older
  versions of Android, define a <a href=
  "{@docRoot}guide/topics/manifest/meta-data-element.html"><code>&lt;meta-data&gt;</code></a>
  name-value pair, where the name is
  <code>"android.support.PARENT_ACTIVITY"</code> and the value is the name of
  the parent activity.
</p>

<p>
  For example, suppose your app has a main activity named
  <code>MainActivity</code> and a single child activity. The following manifest
  code declares both activities, and specifies the parent/child relationship:
</p>
<pre>
&lt;application ... &gt;
    ...

    &lt;!-- The main/home activity (it has no parent activity) --&gt;

    &lt;activity
        android:name="com.example.myfirstapp.MainActivity" ...&gt;
        ...
    &lt;/activity&gt;

    &lt;!-- A child of the main activity --&gt;
    &lt;activity
        android:name="com.example.myfirstapp.MyChildActivity"
        android:label="@string/title_activity_child"
        <strong>android:parentActivityName="com.example.myfirstapp.MainActivity"</strong> &gt;

        &lt;!-- Parent activity meta-data to support 4.0 and lower --&gt;
        &lt;meta-data
            <strong>android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" /&gt;</strong>
    &lt;/activity&gt;
&lt;/application&gt;
</pre>

<h2 id="enable-up">Enable the Up Button</h2>

<p>
  To enable the <em>Up</em> button for an activity that has a parent
  activity, call the app bar's {@link
  android.support.v7.app.ActionBar#setDisplayHomeAsUpEnabled
  setDisplayHomeAsUpEnabled()} method. Typically, you would do this when the
  activity is created. For example, the following {@link
  android.app.Activity#onCreate onCreate()} method sets a {@link
  android.support.v7.widget.Toolbar} as the app bar for
  <code>MyChildActivity</code>, then enables that app bar's <em>Up</em> button:
</p>

<pre>
&#64;Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my_child);

    // my_child_toolbar is defined in the layout file
    Toolbar myChildToolbar =
        (Toolbar) findViewById(R.id.my_child_toolbar);
    setSupportActionBar(myChildToolbar);

    // Get a support ActionBar corresponding to this toolbar
    ActionBar ab = getSupportActionBar();

    // Enable the Up button
    <strong>ab.setDisplayHomeAsUpEnabled(true);</strong>
}
</pre>

<p>
  You do <em>not</em> need to catch the up action in the activity's {@link
  android.app.Activity#onOptionsItemSelected onOptionsItemSelected()} method.
  Instead, that method should call its superclass, as shown in <a href=
  "actions.html#handle-actions">Respond to Actions</a>. The superclass method
  responds to the <em>Up</em> selection by navigating to the parent
  activity, as specified in the app manifest.
</p>