The GCM register() and unregister() methods are blocking. Blocking methods must not be called on the main thread.

The device can't read the response, or there was a 500/503 from the server that can be retried later. The application should use exponential back off and retry.

Specifies scope used in obtaining GCM registrationToken when calling getToken(String, String)

Returned by getMessageType(Intent) to indicate that the server deleted some pending messages because they exceeded the storage limits. The application should contact the server to retrieve the discarded messages.

Returned by getMessageType(Intent) to indicate a regular message.

Returned by getMessageType(Intent) to indicate a send error. The intent includes the message ID of the message and an error code.

Returned by getMessageType(Intent) to indicate a sent message has been received by the GCM server. The intent includes the message ID of the message.

Must be called when your application is done using GCM, to release internal resources.

Return the singleton instance of GCM.

Return the message type from an intent passed into a client app's broadcast receiver. There are two general categories of messages passed from the server: regular GCM messages, and special GCM status messages.

The possible types are:

• MESSAGE_TYPE_MESSAGE—regular message from your server.
• MESSAGE_TYPE_DELETED—special status message indicating that some messages have been discarded because they exceeded the storage limits.
• MESSAGE_TYPE_SEND_ERROR—special status message indicating that there were errors sending one of the messages.

You can use this method to filter based on message type. Since it is likely that GCM will be extended in the future with new message types, just ignore any message types you're not interested in, or that you don't recognize.

Register the application for GCM and return the registration ID. You must call this once, when your application is installed, and send the returned registration ID to the server.

Repeated calls to this method will return the original registration ID.

If you want to modify the list of senders, you must call unregister() first.

Most applications use a single sender ID. You may use multiple senders if different servers may send messages to the app or for testing.

Send an upstream ("device to cloud") message. You can only use the upstream feature if your GCM implementation uses the XMPP-based Cloud Connection Server.

When there is an active connection the message will be sent immediately, otherwise the message will be queued for the maximum interval.

Send an upstream ("device to cloud") message. You can only use the upstream feature if your GCM implementation uses the XMPP-based Cloud Connection Server.

The current limits for max storage time and number of outstanding messages per application are documented in the GCM Developers Guide.

Unregister the application. Calling unregister() stops any messages from the server. This is a blocking call—you shouldn't call it from the UI thread.

You should rarely (if ever) need to call this method. Not only is it expensive in terms of resources, but it invalidates all your registration IDs returned from register() or subscribe(). This should not be done unnecessarily. A better approach is to simply have your server stop sending messages.