Android - Can an activity and a service communicate using the Observer design pattern or similar?

Question

Is it possible to make an activity and a service communicate, using the Observer design pattern? I want to make them communicate both ways by giving them both the role as Observer and Notifier The reason why I want to do this, is that I want low coupling between them. So if the activity crashes for some reason, the service will still be running and still trying to notify the GUI without crashing. The reason I want the service to remain running, is that it acts like a server in a LAN and I still want the system and the clients to communicate even when the GUI of the server is gone.

If this can't be achieved using the Observer pattern or is too complex, is there another way to achieve what I described above?

Thanks in advance

Answer 1

You can run the service as foreground if your are using notification . so when the activity exit the service can update with the notification or remote views.

Also , When you start the activity you can bind the service from the activity to communicate using service connection.

         bindService(new Intent(this,
            YourService.class), mConnection, Context.BIND_AUTO_CREATE);

A started service can use the startForeground(int, Notification) API to put the service in a foreground state, where the system considers it to be something the user is actively aware of and thus not a candidate for killing when low on memory. (It is still theoretically possible for the service to be killed under extreme memory pressure from the current foreground application, but in practice this should not be a concern.)

check the link - http://developer.android.com/reference/android/app/Service.html http://developer.android.com/guide/components/bound-services.html

Answer 2

You could have a communication from Activity to Service with a usual Binder. The Service can inform the Activity about changes with a Callback, which you can register in onServiceConnected() and unregister in the Activities onPause().

With this you have a two way communication between Service and Activity and the implementation isn't to complex.

Answer 3

So if the activity crashes for some reason, the service will still be running

The thing is, Activity doesn't crash. The whole app process does. So if you want to separate Activity and a Service, you need to run them in defferent processes. Note sure about if Service is restarted after process crash, though. Take a look here https://stackoverflow.com/a/12022185/468311, that would be a good start for you.

If this can't be achieved using the Observer pattern or is too complex

As suggested, use Binder. Or you can communicate using Intents.

But keep in mind that Service wasn't intended to be used as a forever-running piece of your app. Try avoding this. Use Service for pereodic background operations.