Tuesday, February 25, 2014

Use minSdkVersion=10 for libraries

I've pushed new versions of microorm and thneed to Maven Central today. The most notable change for both libraries is dropping the support for Android 2.2 and earlier versions. The same change was applied to all Android libraries open sourced by Base. Why? +Jeff Gilfelt summed it up nicely:
This tweet is a good laugh, and an excellent example of what happens if you limit the discussion to 140 characters, but there are poor souls who might need an answer they can use as an objective argument. For them, here is my take on this one: you should drop support for Froyo because sizeable chunk of Java 1.6 APIs were missing from API level 8. I'm not talking about some dark corners of java packages, I'm talking about stuff like String.isEmpty(), Deque, NavigableSet, IOException's constructors with cause parameter, and so on.

Your own code can (and should) be checked with Lint, but these methods and classes can also be used by the 3rd party libraries and I'm not aware of any static analysis tool that can help you in this case. So if your app supports Froyo and uses a lot of external dependencies, you're probably sitting on the NoClassDefFoundError bomb. It might force you to use obsolete versions of libraries, the most notable example of which is Guava - on Froyo you have to use 13.0.1, a 18 months old version.

That's also the reason why the libraries authors should be the first ones to move on to Android 2.3 and later. If you use obsolete library in your application, you're hurting only yourself. If you use it as a library dependency, you're hurting every user of the library.

So move on and bump the minSdkVersion. After all, it's 2014.

Thursday, February 20, 2014

When do you absolutely need WakefulBroadcastReceiver

Yesterdays #AndroidDev #Protip explains how to use WakefulBroadcastReceiver utility class and what problem does it solve, but it doesn't mention a case when using it or manually acquiring WakeLock is essential - using the AlarmManager.

If you're not familiar with AlarmManager's API, here is tl;dr of the docs: it allows you to specify the PendingIntent that should be fired at some point, even if your application is in background. The common use cases for using AlarmManager is for example showing a Notification at the specified time or sending some kind of heartbeat to your backend. In both cases, your code performs potentially long running operation (in case of showing notification you might need some content from your local database), so you don't want to run it in the UI thread. The first thing that comes to mind is to specify an IntentService as a PendingIntent target:
PendingIntent intent = PendingIntent.getService(
  new Intent(context, MyIntentService.class),

AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
  SystemClock.elapsedRealtime() + TimeUnit.MINUTES.toMillis(15)
This code won't always work though. While it is guaranteed that the alarm will go off and the PendingIntent will be sent, because we used a _WAKEUP alarm type, the device is allowed to go back to sleep before the service is started.

It's not explicitly documented, but both +Dianne Hackborn and +CommonsWare confirmed this. The workaround is to use PendingIntent.getBroadcast(), because it is guaranteed that the BroadcastReceiver.onReceive() will be always fully executed before the CPU goes to sleep. Inside that callback you have to acquire WakeLock start your IntentService and release the lock at the end of onHandleIntent() method.

This is where the WakefulBroadcastReceiver comes into play: its startWakefulService and completeWakefulIntent static methods encapsulate all the WakeLocks juggling, allowing you to focus on your business logic.