Ways to guess if C2DM is connected

Question

I\'m trying to place a best guess estimate as to whether C2DM messages can be received.

I\'ve created an application that relies on pushing information to a phone while

Answer 1

Go watch this video, it's a Google I/O talk about C2DM, how to use it and how it works. AFAIK, you can't know if it's connected or not. Probably most of the time they don't even know (until they have to deliver a message and fail).

However, it is highly recommended (in the video as well) that you do not send important data through C2DM (as messages can get lost). The service should only be used as a "network tickle" (with a footprint as small as possible). Your application should be woken up by this tickle and it should start fetching the information it needs itself.

Now, if you implement it this way, it should be easy to implement a polling mechanism. Since you already separated the "tickle" from the actual information retrieval, you can just trigger the retrieval every once in a while if there's no tickle.

Something you can do to check whether C2DM is connected is something like a ping:

1. Send message to phone via C2DM
2. The app receives (or doesn't receive) the message and sends a "pong" back to your server
3. The server waits for the "pong" for a predetermined amount of time (1-2 minutes, I'd say) before marking the device as "offline".

Edit: relying on GTalk is not feasible. GTalk relies on C2DM just like your app, it doesn't have anything "extra". Also, GTalk is not present on all devices. I'm not sure how the GTalk app determines whether it's offline or not (it's not open source, unfortunately), but I'd guess it just tries to ping a server and fails.