G.5 Send Messages to Topics

Topic Messaging

Based on the publish/subscribe model, FCM topic messaging allows you to send a message to multiple devices that have opted in to a particular topic. You compose topic messages as needed, and Firebase handles routing and delivering the message reliably to the right devices.

For example, users of a local weather forecasting app could opt in to a "severe weather alerts" topic and receive notifications of storms threatening specified areas. Users of a sports app could subscribe to automatic updates in live game scores for their favorite teams.

Some things to keep in mind about topics:

• Topic messaging supports unlimited subscriptions for each app.
• Topic messaging is best suited for content such as news, weather, or other publicly available information.
• Topic messages are optimized for throughput rather than latency. For fast, secure delivery to single devices or small groups of devices, target messages to tokens, not topics.
• If you need to send messages to multiple devices per user, consider Device Group messaging for those use cases.

Subscribe the client app to a topic

Client apps can subscribe to any existing topic, or they can create a new topic. When a client app subscribes to a new topic name (one that does not already exist for your Firebase project), a new topic of that name is created in FCM and any client can subsequently subscribe to it.

FCM.listener.addEventListener(FcmEvents.ON_SUBSCRIBE, onSubscribeResult);

// It will take 24 hours before you can see this topic on the Firebase console
FCM.subscribeToTopic("news");

private function onSubscribeResult(e:FcmEvents):void
{
	trace("subscribe to topic " + e.topic + ": " + e.isSuccessful);
}

To unsubscribe, the client app calls Firebase Cloud Messaging unsubscribeFromTopic() with the topic name.

FCM.listener.addEventListener(FcmEvents.ON_UNSUBSCRIBE, onUnsubscribeResult);

FCM.unsubscribeFromTopic("news");

private function onUnsubscribeResult(e:FcmEvents):void
{
	trace("unsubscribe to topic " + e.topic + ": " + e.isSuccessful);
}

NOTICE: When a new topic is created, you will not see that topic in your Firebase console sooner than 24 hours! If you need to check the availability of the newly created topic, you need to send a GET request to https://iid.googleapis.com/iid/info/TOKEN_ID?details=true replacing the TOKEN_ID with the String you received from the FCM.getToken() method. While calling the above request, you need to send the following header also:

Authorization: key=<your-server-key>
content-type: application/json

HINT: You can find your server key in the firebase console: Your project, settings, Project settings, Cloud messaging, Server Key.