ActivityLifecycleCallbacks won't trigger

Question

I'm making a message app and in order to set the status of the user, I have to keep track of the state of my application. When I run the apk, the ActivityLifecycleCallbacks won't trigger, no matter the state of the app. I have tried all the possible fixes that I have found so far but none of them worked out. This is the code:

public class AppState extends Application implements Application.ActivityLifecycleCallbacks {

    @Override
    public void onCreate() {
        super.onCreate();
        Log.e("AppState ", "onCreate");
        registerActivityLifecycleCallbacks(this);
    }

    @Override
    public void onActivityCreated(@NonNull Activity activity, @Nullable Bundle savedInstanceState) {
        Log.e("onActivityCreated", activity.getLocalClassName());
    }

    @Override
    public void onActivityStarted(Activity activity) {
        setLastSeen(KEY_LAST_SEEN_ONLINE);
    }

    @Override
    public void onActivityResumed(@NonNull Activity activity) {
        Log.e("onActivityResumed", activity.getLocalClassName());
    }

    @Override
    public void onActivityPaused(@NonNull Activity activity) {
        Log.e("onActivityPaused", activity.getLocalClassName());
    }

    @Override
    public void onActivityStopped(Activity activity) {
        setLastSeen(String.valueOf(System.currentTimeMillis()));
    }

    @Override
    public void onActivitySaveInstanceState(@NonNull Activity activity, @NonNull Bundle outState) {
        Log.e("omInstanceState", activity.getLocalClassName());
    }

    @Override
    public void onActivityDestroyed(@NonNull Activity activity) {
        Log.e("onActivityDestroyed", activity.getLocalClassName());
    }

    private void setLastSeen(String lastSeen) {
        FirebaseDatabase.getInstance().getReference(KEY_COLLECTION_USERS)
                .child(FIREBASE_USER.getUid())
                .child(KEY_LAST_SEEN)
                .setValue(lastSeen);
    }
}

For the sake of clarifying, I have been reading the documentation and some other tweaks and none of them made reference to implementing code on some other class of my project so I assume that the problem would be within this class. Thank you for your time :)

Answer 1

Check if you register your AppState application class in manifest :

 <application
        android:name=".AppState"
        ...