ActionBar（官方文档学习记录三）

Adding an Up Action

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This lesson teaches you to

Declare a Parent Activity

Enable the Up Button

See Also

Providing Up Navigation

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 Up button on the app bar for all activities except the main one. When the user selects the Up button, the app navigates to the parent activity.

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

Declare a Parent Activity

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

android:parentActivityName

attribute.

The

android:parentActivityName

attribute was introduced in Android 4.1 (API level 16). To support devices with older versions of Android, define a

<meta-data>

name-value pair, where the name is

"android.support.PARENT_ACTIVITY"

and the value is the name of the parent activity.

For example, suppose your app has a main activity named

MainActivity

and a single child activity. The following manifest code declares both activities, and specifies the parent/child relationship:

<application ... >
...

<!-- The main/home activity (it has no parent activity) -->

<activity
android:name="com.example.myfirstapp.MainActivity" ...>
...
</activity>

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

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

Enable the Up Button

To enable the Up button for an activity that has a parent activity, call the app bar's

setDisplayHomeAsUpEnabled()

method. Typically, you would do this when the activity is created. For example, the following

onCreate()

method sets a

Toolbar

as the app bar for

MyC
3ff8
hildActivity

, then enables that app bar's Up button:

@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
ab.setDisplayHomeAsUpEnabled(true);
}

You do not need to catch the up action in the activity's

onOptionsItemSelected()

method. Instead, that method should call its superclass, as shown in Respond to Actions. The superclass method responds to the Up selection by navigating to the parent activity, as specified in the app manifest.