How to automatically open app when receive push notification?

Question

I want to automatically open app when receive push notification. I\'ve tried but it still does not work as I expected. This code below is work when the app is active or in M

Answer 1

int requestID = (int) System.currentTimeMillis();
Intent notificationIntent = new Intent(getApplicationContext(), NotificationActivity.class);

notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP); 

PendingIntent contentIntent = PendingIntent.getActivity(this, requestID,notificationIntent, PendingIntent.FLAG_UPDATE_CURRENT);

And add PendingIntent like this

notificationBuilder = new NotificationCompat.Builder(this)
            .setContentTitle("Notification")
            .setSmallIcon(R.mipmap.icon_notif)
            .setContentText(messageBody)
            .setContentIntent(contentIntent);
            .setPriority(NotificationCompat.PRIORITY_MAX)
            .setDefaults(Notification.DEFAULT_LIGHTS );