How to catch lifecycle events with ProcessLifecycleOwner?

Question

I am trying to (at least partially) determine when an application gets closed by the user to release some connections, etc. To do this, I am using the ProcessLifecycleOwner with my application class implementing LifecycleObserver. Despite taking the starting code from tutorials and other helpful articles, it does not seem to detect any lifecycle events.

Most of the code came from this example.

My application class:

public class App extends Application implements LifecycleObserver {
    @Override
    public void onCreate() {
        super.onCreate();

        ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    public void created() {
        Log.d("SampleLifeCycle", "ON_CREATE");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void started() {
        Log.d("SampleLifeCycle", "ON_START");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    public void resumed() {
        Log.d("SampleLifeCycle", "ON_RESUME");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    public void paused() {
        Log.d("SampleLifeCycle", "ON_PAUSE");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    public void stopped() {
        Log.d("SampleLifeCycle", "ON_STOP");
    }
}

The dependency in Gradle

dependencies {
    //...
    implementation 'android.arch.lifecycle:extensions:1.1.1'
}

So far, this code has not logged a single event of any sort, whether the app is entering the foreground or the background.

EDIT

Note: You NEED to declare your application in the Manifest for anything to work in your custom application class.

Answer 1

You need the corresponding annotation processor to pay attention to those annotations:

annotationProcessor 'android.arch.lifecycle:compiler:1.1.1'

Or, enable Java 8 support, and switch to DefaultLifecycleObserver.