I am writing an Android app, finally (yay me) and for this app I need persistant, but user closeable, network sockets (yes, more than one). I decided to try my hand at writing my own version of an IRC Client.
My design issue however, is I’m not sure how to run the Socket connectivity itself. If I put the sockets at the Activity level, they keeps getting closed shortly after the Activity becomes non-visible (also a problem that needs solving…but I think i figured that one out)…but if I run a “connectivity service”, I need to find out if I can have multiple instances of it running (the service, that is…one per server/socket). Either that or a I need a way to Thread the sockets themselves and have multiple threads running that I can still communicate with directly (ID system of some sort).
Thus the question: Is it a ‘better’, or at least more “proper” design pattern, to put the Socket and networking in a service, and have the Activities consume said service…or should I tie the sockets directly to some Threaded Process owned by the UI Activity and not bother with the service implementation at all? I do know better than to put the networking directly on the UI thread, but that’s as far as I’ve managed to get.
1
The answer is Service + Thread.
Don’t put the socket in an Activity. The activity is for UI. It gets recreated when the user rotates the phone. You can run into problems when the user receives a phone call.
Put your sockets in a Service. Your activity/activities can bind to the Service and use it’s methods. Or you can use a Messenger to communicate between an Activity and the Service.
Services on Android run in the UI thread so in the Service you’ll need your own thread for the socket communication.
Just a suggestion (something I haven’t yet tried w/Android, but should work).
Try putting a WebView in your main activity (so it won’t die when you switch child activities) which includes a full DOM document and a child iframe element. Set the iframe’s src attribute to a comet service you define, with a keep-alive header. Push the messages using comet. Works like a charm in chrome. If your back end doesn’t support comet, you can set it up manually.