Android Cloud to Device Messaging (C2DM) is deprecated. The C2DM service will continue to be maintained in the short term, but C2DM will accept no new users, and it will grant no new quotas. C2DM developers are strongly encouraged to move to Google Cloud Messaging (GCM). GCM is the next generation of C2DM.
This document is addressed to C2DM developers who are moving to GCM. It describes the differences between GCM and C2DM, and explains how to migrate existing C2DM apps to GCM.
C2DM was launched in 2010 to help Android apps send data from servers to their applications. Servers can tell apps to contact the server directly, to fetch updated application or user data. The C2DM service handles all aspects of queueing of messages and delivery to the target application running on the target device.
GCM replaces C2DM. The focus of GCM is as follows:
GCM builds on the core foundation of C2DM. Here is what's different:
collapse_key parameter and messages will not be collapsed. GCM will store up to 100 messages. If you exceed that number, all messages will be discarded but you will receive a special message. If an application receives this message, it needs to sync with the server. For more information, see Advanced Topics.GCM also provides client and server helper libraries to make writing your code easier.
C2DM and GCM are not interoperable. For example, you cannot post notifications from GCM to C2DM registration IDs, nor can you use C2DM registration IDs as GCM registration IDs. From your server-side application, you must keep keep track of whether a registration ID is from C2DM or GCM and use the proper endpoint.
As you transition from C2DM to GCM, your server needs to be aware of whether a given registration ID contains an old C2DM sender or a new GCM project number. This is the approach we recommend: have the new app version (the one that uses GCM) send a bit along with the registration ID. This bit tells your server that this registration ID is for GCM. If you don't get the extra bit, you mark the registration ID as C2DM. Once no more valid registration IDs are marked as C2DM, you can complete the migration.
This section describes how to move existing C2DM apps to GCM.
Migration is simple! The only change required in the application is replacing the email account passed in the sender parameter of the registration intent with the project number generated when signing up for the new service. For example:
Intent registrationIntent = new Intent("com.google.android.c2dm.intent.REGISTER");
// sets the app name in the intent
registrationIntent.putExtra("app", PendingIntent.getBroadcast(this, 0, new Intent(), 0));
registrationIntent.putExtra("sender", senderID);
startService(registrationIntent);
After receiving a response from GCM, the registration ID obtained must be sent to the application server. When doing this, the application should indicate that it is sending a GCM registration ID so that the server can distinguish it from existing C2DM registrations.
When the application server receives a GCM registration ID, it should store it and mark it as such.
Sending messages to GCM devices requires a few changes:
https://android.googleapis.com/gcm/send.For example:
Content-Type:application/json
Authorization:key=AIzaSyB-1uEai2WiUapxCs2Q0GZYzPu7Udno5aA
{
"registration_id" : "APA91bHun4MxP5egoKMwt2KZFBaFUH-1RYqx...",
"data" : {
"Team" : "Portugal",
"Score" : "3",
"Player" : "Varela",
},
}
For a detailed discussion of this topic and more examples, see the Architectural Overview.
Eventually, once enough users of your application have migrated to the new service, you might want to take advantage of the new JSON-formatted requests that give access to the full set of features provided by GCM.