https://developer.android.com/training/implementing-navigation/temporal.html#SynthesizeBackStack

Ordinarily, the system incrementally builds the back stack as the user navigates from one activity to the next. However, when the user enters your app with a deep link that starts the activity in its own task, it’s necessary for you to synthesize a new back stack because the activity is running in a new task without any back stack at all.

For example, when a notification takes the user to an activity deep in your app hierarchy, you should add activities into your task’s back stack so that pressing Back navigates up the app hierarchy instead of exiting the app. This pattern is described further in the Navigation design guide

當一個通知將用戶帶到你的應用程序層次結構中的活動時，你應該將活動添加到你的任務的後棧中，這樣你就可以在你的應用程序層次上進行反向操作，而不是退出應用程序.

Beginning in Android 4.1 (API level 16), you can declare the logical parent of each activity by specifying the android:parentActivityName attribute in the 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 element inside the . Then specify the parent activity as the value for android.support.PARENT_ACTIVITY, matching the android:parentActivityName attribute.

<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.DisplayMessageActivity"
        android:label="@string/title_activity_display_message"
        android:parentActivityName="com.example.myfirstapp.MainActivity" >
        <!-- The meta-data element is needed for versions lower than 4.1 -->
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" />
    </activity>
</application>

點擊通知，將父類加入回退棧中

// 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);

fragment回退棧

If your application updates other user interface elements to reflect the current state of your fragments, such as the action bar, remember to update the UI when you commit the transaction. You should update your user interface after the back stack changes in addition to when you commit the transaction. You can listen for when a FragmentTransaction is reverted by setting up an FragmentManager.OnBackStackChangedListener:

監聽WebView回退

@Override
public void onBackPressed() {
if (mWebView.canGoBack()) {
mWebView.goBack();
return;
}
// Otherwise defer to system default behavior.
super.onBackPressed();
}