Firebase Cloud Messaging(FCM)主题消息传递可让您向选择加入特定主题的多个设备发送消息.基于发布/订阅模型，主题消息支持每个应用程序的无限制订阅，即您的组被附加到新闻组，体育组等特定主题.

Firebase Cloud Messaging (FCM) topic messaging allows you to send a message to multiple devices that have opted in to a particular topic. Based on the publish/subscribe model, topic messaging supports unlimited subscriptions for each app i.e your group is attached to specific topic like news group,sports group etc.

FirebaseMessaging.getInstance().subscribeToTopic("news");

退订unsubscribeFromTopic("news")

从服务器端，您需要设置特定主题，即像这样的一组用户:

From Server side you need to set up for specif topic i.e a group of user like this:

https://fcm.googleapis.com/fcm/send
Content-Type:application/json
Authorization:key=AIzaSyZ-1u...0GBYzPu7Udno5aA

{
  "to": "/topics/news",
  "data": {
    "message": "This is a Firebase Cloud Messaging Topic Message!",
   }
}

"/topics/news"这将向订阅新闻主题的人群发送通知

"/topics/news" This will send notification to group of people who have subsribe the news topic