Feb 12, 2009
I'm an experienced C++/Java dev who has been truly enjoying that past two days of getting neck deep into the Android SDK. I can foresee a lot of sleepless nights ahead Now, being arrogant due to experience (lol) I basically wrote a hello world Activity, got it to work and promptly decided to write an out of process service with accompanying client for project #2. Android is so well thought out (if not exactly documented although that's an 'over time' issue inmho) that I had basically implented everything but callbacks into the client before realizing (and feeling like a total idiot) that there's a very nice example called RemoteService (lol @ me - again) Basically, this validated everything I'd been doing, although I did notice that because my client is in its own project and namespace and my service is in another project and namespace (but the same Eclipse workspace) that I had to have the service entry in my service's manifest AND my client's manifest (that one took me a while to figure out) in order to bind on the service. Anyhow, everything's great, I am starting to love on Android (figuratively) but I've run into <BRITISH-NESS>a bit of a sticky wicket, eh, wot?</BRITISH-NESS>.
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When my client Activity binds on my service (which is running in its own process) and calls the equivalent of 'registerCallback', the interface is added perfectly to the RemoteCallbackList object and I can immediately (right on the next line of code) use the interface to send a notification to the client. Now, my problem is that when my main service thread tries to pull the interface out of the RemoteCallbackList via the broadcast methods, the RemoteCallbackList is always 'empty' - it returns 0 from beginBroadcast. After double checking ensure that I AM actually adding it to the list (because I've been a collossal idiot before) and that I am getting success back from 'register', I immediately think it's a threading issue, so: I add logging code to the service in key places to log what the thread id is repeatedly, and I think "uh, I think I need to use a handler of some sort to make the call back in the thread that handled the registration" and to double check I call beginBroadcast right after 'register' and find that it always returns back the correct number of callback interfaces. So it VERY much appears to be a threading issue (to me) so now I'm a bit stuck I've written a handler so that my main service thread can request the correct thread to actually call 'beginBroadcast' and then thought 'how is it going to know what thread that is...?' and instead am now thinking I need to pass, via a handler or something, the incoming interface from the thread that runs when the client calls the equivalent of 'registerCallback' to my main service thread. What part of the proper paradigm am I missing? BTW, as an example of the thread IDs, my main service thread is #1, the runnable I use for tasks in the main service thread shows an ID of #1, the message handler I was thinking I could use, shows an ID of #1, but the thread ID I get in my code in the service that runs when the user registers their callback is #7.
If I plan to notify clients when the service notices something it thinks they need to know, do I need to notify (somehow) the clients via the thread with ID #7 or do I need to pass the interface I get when the user registers their callback from thread #7 to thread #1 and call 'register' on the RemoteCallbackList from thread #1? Sorry for the verbosity but I figured more is better than less. Again, everything works great except this one little part.