解决方案:

1. 如果您是从Firebase控制台发送推送通知&您的应用处于后台或已被杀死，则不会调用 MyFirebaseMessagingService . (firebase文档中未提及)

如果您是从Firebase控制台发送推送通知&您的应用程序处于前台，则 MyFirebaseMessagingService 将被调用.

If you are sending push notification from firebase console & your app is in foreground then MyFirebaseMessagingService will get called.

如果您要从服务器发送推送通知(我的意思是后端，即网站或某些基于Web的仪表板)，您的应用处于后台，处于死机状态或处于前台，则 MyFirebaseMessagingService 将被调用.

If you are sending push notification from your server(I mean back-end i.e a website or some web based dashboard) & your app is in background or kill or in foreground then MyFirebaseMessagingService will get called.