Clarification of AlarmManager behavior in Android

问题:

I see all the examples of AlarmManager being set by an Activity.

My question is this: If my application sets a recurring AlarmManager, does that persist even after the application that started is is closed and removed from memory?

If not, how do I start an AlarmManager at a lower level that is started by Android at boot up and if it ever fails or dies or throws an exception is restarted without the user having to do anything?

Lastly, if the action I wish for the BroadcastReceiver to undertake has no visual components, do I still have to create a separate Activity for it? In my case I want there to be a background uploader that wakes up and looks into a folder and if it sees files in that folder, sends them off to the server. I don't need any feedback to the user.

So, my ideal would be to have a magical, OS based AlarmManager that calls an IntentService which just handles the uploading, but I'm unclear on how to get such an AlarmManager running in the first place.

TIA

回答1:

Yes, AFAIK the alarms "survive" and keeps getting triggered, even after the activity that registered them ends. But they don't survive a phone reboot.

If I understands your problem correctly, I think you can achieve what your looking for by creating a project with a broadcast receiver that listens for android.intent.action.BOOT_COMPLETED intents and then (re-)register a repeating alarm, which in turns starts a (Intent)Service to do the uploading.

You don't need an activity, but you probably would want one anyway, to let the user temporarily disable the upload mechanism by checking off a checkbox, or something. It would probably also be nice to let the user choose the frequency of your alarm, i.e. how often the service should be started and look for new files to upload. This would also be a good place to register your alarm for the first time.

回答2:

I agree with Nicolai that you'd have 2 broadcast receivers in your application :

• one that re-register the alarm on boot
• one that starts your service when triggered by the alarm

You could still have an activity but it shouldn't be started by the alarm receiver (hence the service) : instead, maybe launch a notification as you start your service, with the user having the possibility to launch the activity from the expanded message of the notification.

maybe also think about setInexactRepeating (instead of setRepeating) for your alarm, as well as using a worker thread to handle the long uploads (in case the user wants to use your activity in the main thread at the same time).