Questions tagged [google-cloud-messaging]

Firebase Cloud Messaging (FCM) is the new version of GCM. It inherits the reliable and scalable GCM infrastructure, plus new features! See the FAQ to learn more. If you are integrating messaging in a new app, start with FCM. GCM users are strongly recommended to upgrade to FCM, in order to benefit from new FCM features today and in the future. See the FCM tag.

Google Cloud Messaging (GCM) is a free service that enables developers to send messages between servers and client apps. This includes downstream messages from servers to client apps, and upstream messages from client apps to servers. The GCM service handles all aspects of queueing of messages and delivery to client applications running on target devices, and it is completely free.

The service provides a simple, lightweight mechanism that servers can use to tell mobile applications to contact the server directly, to fetch updated application or user data. The service handles all aspects of enqueuing of messages and delivery to the target application running on the target device.

The free service has the ability to send a lightweight message informing the Android application of new data to be fetched from the server. Larger messages can be sent with up to 4 KB of payload data. Each notification message size is limited to 1024 bytes, and Google limits the number of messages a sender sends in aggregate, and the number of messages a sender sends to a specific device.

For example, a lightweight downstream message could inform a client app that there is new data to be fetched from the server, as in the case of a "new email" notification. For use cases such as instant messaging, a GCM message can transfer up to 4kb of payload to the client app. The GCM service handles all aspects of queueing of messages and delivery to and from the target client app.

Send messages from the cloud

Send a message using GCM HTTP connection server protocol:

  https://gcm-http.googleapis.com/gcm/send
  Content-Type:application/json
  Authorization:key=AIzaSyZ-1u...0GBYzPu7Udno5aA
  {
    "to": "/topics/foo-bar",
    "data": {
      "message": "This is a GCM Topic Message!",
     }
  }

Handle a downstream message on an Android device:

  @Override
  public void onMessageReceived(String from, Bundle data) {
     String message = data.getString("message");
     Log.d(TAG, "From: " + from);
     Log.d(TAG, "Message: " + message);
     // Handle received message here.
  }