android-Providing Up Navigation,Providing Proper Back Navigation

 All screens in your app that are not the main entrance to your app (the "home" screen) should offer the user a way to navigate to the logical parent screen in the app's hierarchy by pressing the Up button in the action bar.

 >Beginning in Android 4.1 (API level 16), you can declare the logical parent of each activity by specifying theandroid:parentActivityName attribute in the <activity> element.

If your app supports Android 4.0 and lower, include the Support Library with your app and add a <meta-data>element inside the <activity>. Then specify the parent activity as the value forandroid.support.PARENT_ACTIVITY, matching the android:parentActivityName attribute.

>

<!-- A child of the main activity -->
    <activity
        android:name="com.example.myfirstapp.DisplayMessageActivity"
        android:label="@string/title_activity_display_message"
        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>

> If the target parent activity is in the task's back stack, it is brought forward. The way it is brought forward depends on whether the parent activity is able to handle an onNewIntent() call:

• If the parent activity has launch mode <singleTop>, or the up intent contains FLAG_ACTIVITY_CLEAR_TOP, the parent activity is brought to the top of the stack, and receives the intent through its onNewIntent()method.
• If the parent activity has launch mode <standard>, and the up intent does not containFLAG_ACTIVITY_CLEAR_TOP, the parent activity is popped off the stack, and a new instance of that activity is created on top of the stack to receive the intent.

 You can do so by first calling shouldUpRecreateTask() to check whether the current activity instance exists in a different app's task. If it returns true, then build a new task with TaskStackBuilder. Otherwise, you can use the navigateUpFromSameTask() method as shown above.

For example:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    // Respond to the action bar's Up/Home button
    case android.R.id.home:
        Intent upIntent = NavUtils.getParentActivityIntent(this);
        if (NavUtils.shouldUpRecreateTask(this, upIntent)) {
            // This activity is NOT part of this app's task, so create a new task
            // when navigating up, with a synthesized back stack.
            TaskStackBuilder.create(this)
                    // Add all of this activity's parents to the back stack
                    .addNextIntentWithParentStack(upIntent)
                    // Navigate up to the closest parent
                    .startActivities();
        } else {
            // This activity is part of this app's task, so simply
            // navigate up to the logical parent activity.
            NavUtils.navigateUpTo(this, upIntent);
        }
        return true;
    }
    return super.onOptionsItemSelected(item);
}

 Note: In order for the addNextIntentWithParentStack() method to work, you must declare the logical parent of each activity in your manifest file, using the android:parentActivityName attribute (and corresponding <meta-data> element) as described above.

>Providing Proper Back Navigation

 Back navigation is how users move backward through the history of screens they previously visited. All Android devices provide a Back button for this type of navigation, so your app should not add a Back button to the UI.

Navigation patterns that require you to manually specify the Back behavior include:
 When the user enters a deep-level activity directly from a notification, an app widget, or the navigation drawer.
Certain cases in which the user navigates between fragments.
When the user navigates web pages in a WebView.

 》Beginning in Android 4.1 (API level 16), you can declare the logical parent of each activity by specifying theandroid:parentActivityName attribute in the <activity> element. This allows the system to facilitate navigation patterns because it can determine the logical Back or Up navigation path with this information.

If your app supports Android 4.0 and lower, include the Support Library with your app and add a <meta-data>element inside the <activity>. Then specify the parent activity as the value forandroid.support.PARENT_ACTIVITY, matching the android:parentActivityName attribute.

 Adding activities to the back stack begins upon the event that takes the user into your app. That is, instead of calling startActivity(), use the TaskStackBuilder APIs to define each activity that should be placed into a new back stack. Then begin the target activity by calling startActivities(), or create the appropriatePendingIntent by calling getPendingIntent().

For example, when a notification takes the user to an activity deep in your app hierarchy, you can use this code to create a PendingIntent that starts an activity and inserts a new back stack into the target task:

// Intent for the activity to open when user selects the notification
Intent detailsIntent = new Intent(this, DetailsActivity.class);

// Use TaskStackBuilder to build the back stack and get the PendingIntent
PendingIntent pendingIntent =
        TaskStackBuilder.create(this)
                        // add all of DetailsActivity's parents to the stack,
                        // followed by DetailsActivity itself
                        .addNextIntentWithParentStack(upIntent)
                        .getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);

NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
builder.setContentIntent(pendingIntent);

The resulting PendingIntent specifies not only the activity to start (as defined by detailsIntent), but also the back stack that should be inserted into the task (all parents of the DetailsActivity defined bydetailsIntent). So when the DetailsActivity starts, pressing Back navigates backward through each of theDetailsActivity class's parent activities.

Note: In order for the addNextIntentWithParentStack() method to work, you must declare the logical parent of each activity in your manifest file, using the android:parentActivityName attribute (and corresponding <meta-data> element) as described above.

 Note: You should not add transactions to the back stack when the transaction is for horizontal navigation (such as when switching tabs) or when modifying the content appearance (such as when adjusting filters). For more information, about when Back navigation is appropriate, see the Navigation design guide.

 If a part of your application is contained in a WebView, it may be appropriate for Back to traverse browser history. To do so, you can override onBackPressed() and proxy to the WebView if it has history state:

@Override
public void onBackPressed() {
    if (mWebView.canGoBack()) {
        mWebView.goBack();
        return;
    }

    // Otherwise defer to system default behavior.
    super.onBackPressed();
}