Android: how to know if your app is completely hidden

AndroidApplication.java

public class AndroidApplication extends MultiDexApplication {
    public static final String TAG = AndroidApplication.class.getSimpleName();

    @Override
    public void onCreate() {
        super.onCreate();
        registerComponentCallbacks(new ComponentCallback());
    }

    private class ComponentCallback implements ComponentCallbacks2 {
        @Override
        public void onTrimMemory(int level) {
            if(level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
                Log.d(TAG, "Application not visible anymore");
            } else if (level == ComponentCallbacks2.TRIM_MEMORY_COMPLETE) {
                Log.d(TAG, "Application is going to be killed");
            }
        }

        @Override
        public void onLowMemory() {
            onTrimMemory(TRIM_MEMORY_COMPLETE);
        }

        @Override
        public void onConfigurationChanged(Configuration newConfig) {
            //no op
        }
    }
}