AppStatus.java

public class MyApp extends Application {

    private AppStatus mAppStatus = AppStatus.FOREGROUND;

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

        registerActivityLifecycleCallbacks(new MyActivityLifecycleCallbacks());
    }

    public MyApp get(Context context) {
        return (MyApp) context.getApplicationContext();
    }

    public AppStatus getAppStatus() {
        return mAppStatus;
    }

    // check if app is foreground
    public boolean isForeground() {
        return mAppStatus.ordinal() > AppStatus.BACKGROUND.ordinal();
    }

    public enum AppStatus {
        BACKGROUND,                // app is background
        RETURNED_TO_FOREGROUND,    // app returned to foreground(or first launch)
        FOREGROUND;                // app is foreground
    }

    public class MyActivityLifecycleCallbacks implements ActivityLifecycleCallbacks {

        // running activity count
        private int running = 0;

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

        }

        @Override
        public void onActivityStarted(Activity activity) {
            if (++running == 1) {
                // running activity is 1,
                // app must be returned from background just now (or first launch)
                mAppStatus = AppStatus.RETURNED_TO_FOREGROUND;
            } else if (running > 1) {
                // 2 or more running activities,
                // should be foreground already.
                mAppStatus = AppStatus.FOREGROUND;
            }
        }

        @Override
        public void onActivityResumed(Activity activity) {
        }

        @Override
        public void onActivityPaused(Activity activity) {
        }

        @Override
        public void onActivityStopped(Activity activity) {
            if (--running == 0) {
                // no active activity
                // app goes to background
                mAppStatus = AppStatus.BACKGROUND;
            }
        }

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

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