Android Application class for adding iOS didBecomeActive callback method

StateAwareApplication.java

import android.app.Activity;
import android.app.Application;
import android.os.Bundle;

import java.util.Date;

/**
 * Simple Application providing didBecomeActive callback method.
 */
public abstract class StateAwareApplication extends Application implements Application.ActivityLifecycleCallbacks {

    private static Date lastActiveAt = new Date();

    private static boolean activityVisible;

    @Override
    public void onCreate() {
        super.onCreate();

        lastActiveAt.setTime(0);

        registerActivityLifecycleCallbacks(this);
    }

    /**
     * Caution: this will be called sometime after the (first) activity's onResume
     */
    public abstract void didBecomeActive();

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) { }

    @Override
    public void onActivityStarted(Activity activity) { }

    @Override
    public void onActivityResumed(Activity activity) {
        if (!activityVisible && (new Date().getTime() - lastActiveAt.getTime() > 4000)) {
            didBecomeActive();
        }
        activityVisible = true;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        lastActiveAt = new Date();
        activityVisible = false;
    }

    @Override
    public void onActivityStopped(Activity activity) {
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
    }
}