Android - update widget over service with data from network. Best approach?

Question

I have a question regarding Android widgets and especially Android services. Here is what I want to do: On the phone the user should be able to add my widget to his homescreen. The widget gets its data from network. After reading some tutrials about this, I found out that the best approach would be to create a service that gets the data from network (TCP sockets) and then updates the widget constantly. That is done with ScheduledExecutorService which executes a Runnable in a certain interval. The Runnable will connect to a server, get the data and should update the widget).

My problem is now, that the widget don't need to be updated when the screen is off and so the service should not run because of battery drain. My question is: How to do it the best way?

I found 2 approaches which would more or less do what I want:

1. When the first instance of the widget is added to homescreen, it will register a Broadcast Receiver that receives the ACTION_SCREEN_ON and ACTION_SCREEN_OFF intent action from Android OS. If ACTION_SCREEN_ON is fired, it will start the updater service, otherwise it will stop it. But I'm really unsure if that's a good approach because of the broadcast receiver lifetime.

2. In the updater service's Runnable, which is executed periodically by the ScheduledExecutorService and actually does the network stuff, I check via PowerManager.isScreenOn(), if the screen is on. If yes, I execute the network code, otherwise not. But what is when the device is in standby? Is this code executed then? What about battery drain here?

Is there maybe a "best practice" approach for what I want to do? I've read alot about the AlarmManager and that it is a very powerful tool. Can you schedule tasks with this in the way, that they are only executed when the display is on?

Thanks for your help.

Best Regards NiThDi

Answer 1

Your first solution (widget handling screen ON and OFF broadcasts) to the problem is the way to go. Start a new IntentService for a background communication to your application server. Once it finished, send your custom "Completed" broadcast with results and then handle it in your widget.

As an additional benefit it would allow multiple instances of your widget to work from one "source" and would not consume any resources in case user did not add any widgets.

UPDATE As it is impossible to use screen ON/OFF broadcasts with a widget, I would probably use this (AlarmManager with an ELAPSED_REALTIME (not ELAPSED_REALTIME_WAKEUP) alarm) to schedule an (intent) service run. This way your service will not be scheduled when screen is off, but will run periodically when it is on. And if the delay between screen ON and OFF is more than the period it will run immediately on screen coming back ON.

As for your question about broadcast receivers lifetime, as said before, use IntentService for a long running task and then broadcast your results back from it. When you starting a service that call does not block so broadcast receiver will finish in a timely matter.

UPDATE 2 According to this screen OFF does not mean device is sleeping. You already have a solution to this issue by using PowerManager.isScreenOn().