android - How to handle notifications with FCM when app is in either foreground or background

Question

I used firebase to build My project.
It will also use the FCM (firebase cloud message).
But there is a problem.
I can't handle the FCM (create my custom notificaion) when app is in background.

The official site tutorial said that
case 1: App foreground -> override the "onMessageReceived()" to create your custom notification.
case 2: App background -> System will create the notification directly. We needn't and can't do anything. Because it doesn't trigger the "onMessageReceived()" in this case.

However if I can do nothing when app is background, I can't create my custom notification. (e.g. After Users click the notification and it will pop up a window to show detail information.)

So how do I handle notifications with FCM when app is in background?

Answer 1

Waitting for answers