Backstack not cleared when notification clicked

Question

I'm using Firebase Cloud Messenger (FCM) to push notifications to my app. The notifications are received when the app is in the background so onMessageReceived is not triggered as the notification doesn't have a payload (data). Everything is fine with that but it means I can't create my own notification as everything is automatically handled by System tray.

When I click the notification I expect the entire backstack to be cleared and the app to restart from scratch. Basically I want the opposite of this post. This is supposed to be the default behaviour.

However, when I click on the notification, if the app was already opened, the app restarts from the launcher but on top of the existing backstack.

For instance if you have:

HomeScreen -> Page1

when the notification is clicked, you now have in the stack:

HomeScreen -> Page1 -> HomeScreen

when it's supposed to only be:

HomeScreen

My launcher is an Activity only displayed when the app starts so I don't want it to be kept in the backstack. I turns out this this why I get this issue. So basically if the Launcher Activity calls finish() on itself and/or has noHistory="true" set in the Manifest, the backstack is not cleared when the notification is clicked.

How can I solve this issue?

Answer 1

I found a solution. The idea is to create a new LauncherActivity in charge of launching the existing one and clearing the backstack in the process.

There are probably other ways to do that but I wanted to keep the original Launcher with noHistory="true" as otherwise I have issue with the transition animation with the next Activity if I implemented the below solution directly to it.

The new Launcher is called StartActivity

In the Manifest:

<activity
    android:name=".StartActivity"
    android:screenOrientation="portrait"
    android:theme="@style/AppTheme">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

The Activity:

public class StartActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Intent intent = new Intent(this, LauncherActivity.class);
        // Add the flags to clear the stack
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
        // Start the intent with a defined transition animation. The animation is not 
        // required but it make the transition seamless.
        startActivity(intent, getFadeInOutAnimation(this));

        // Necessary for the app not to crash. Basically just a FrameLayout
        setContentView(R.layout.activity_start);
    }

    public static Bundle getFadeInOutAnimation(Context context) {
        // Allows us to display a fading animation as transition between the activities.
        // The animation can be whatever you want
        return ActivityOptions.makeCustomAnimation(context,
                R.anim.fade_in, R.anim.fade_out).toBundle();
    }
}