ActivityLifecycleListener

ActivityLifecycleListener.java

import android.app.Activity;

import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;

import java.lang.ref.WeakReference;
import java.util.function.Consumer;

public class ActivityLifecycleListener implements LifecycleObserver {

    private int resumeCount = 0;
    private WeakReference<Activity> activityReference;
    private Consumer<Activity> onMoveToForeground;
    private Consumer<Activity> onMoveToBackground;

    public void setOnMoveToForeground(Consumer<Activity> onMoveToForeground) {
        this.onMoveToForeground = onMoveToForeground;
    }

    public void setOnMoveToBackground(Consumer<Activity> onMoveToBackground) {
        this.onMoveToBackground = onMoveToBackground;
    }

    public ActivityLifecycleListener(Activity activity) {
        this.activityReference = new WeakReference<>(activity);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    void onMoveToForeground() { // app moved to foreground
        resumeCount++;
        if(resumeCount == 1) return;

        if(onMoveToForeground != null) onMoveToForeground.accept(activityReference.get());
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    void onMoveToBackground() { // app moved to background
        if(onMoveToBackground != null) onMoveToBackground.accept(activityReference.get());
    }
}

/*
ActivityLifecycleListener activityLifecycleListener = new ActivityLifecycleListener(this);
activityLifecycleListener.setOnMoveToBackground(activity -> {
    Toast.makeText(activity, "onMoveToBackground", Toast.LENGTH_SHORT).show();
});
activityLifecycleListener.setOnMoveToForeground(activity -> {
    Toast.makeText(activity, "onMoveToForeground", Toast.LENGTH_SHORT).show();
});
ProcessLifecycleOwner
        .get()
        .getLifecycle()
        .addObserver(activityLifecycleListener);
*/