How to detect previous Activity when app go to background

Question

I have 2 activities : ActivityA and ActivityB.
When application go to background I want to detect which Activity has just been on foreground.
For example : Activity A is in foreground -> Click home button -> App go to background

onBackground: ActivityA

Activity B is in foreground -> Click home button -> App go to background

onBackground: ActivityB

I confused about ProcessLifecycleObserver

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onEnterForeground() {
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onEnterBackground() {
    }

because of can not detect which Activity here ?

And when I try to use ActivityLifecycleCallbacks it's activity lifecycle , not application lifecycle so background state can not detected here.

Does any one has solution for that case ?

Answer 1

You should use the android.arch.lifecycle package which provides classes and interfaces that let you build lifecycle-aware components.

For example:

public class MyApplication extends Application implements LifecycleObserver {

    String currentActivity;

    @Override
    public void onCreate() {
        super.onCreate();
        ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    private void onAppBackgrounded() {
        Log.d("MyApp", "App in background");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    private void onAppForegrounded() {
        Log.d("MyApp", "App in foreground");
    }

    public void setCurrentActivity(String currentActivity){
        this.currentActivity = currentActivity;
    }
}

In your activities's onResume() method, you can then maintain the currentActivity variable in your MyApplication singleton instance:

@Override
protected void onResume() {
    super.onResume();
    MyApplication.getInstance().setCurrentActivity(getClass().getName());
}

And check the currentActivity attribute value in onAppBackgrounded().