AlarmManager vs Handler.postDelayed

Question

In a service which method of delayed execution to be used handler.postdelayed or Alarmmanager. what are the pro and cons.

I have 2 services (a) which does background processing and updates the UI via a boradcast message (b) which does some calculation and updates the homescreen widget every 5 secs.

Thanks

Answer 1

I found this note in Android Developer's site:

http://developer.android.com/training/scheduling/alarms.html

It seems that AlarmManager would be the class to use for starting services.

Regarding Handlers it states that:

"For timing operations that are guaranteed to occur during the lifetime of your application, instead consider using the Handler class in conjunction with Timer and Thread. This approach gives Android better control over system resources."

Answer 2

I would suggest you do this with RxJava. In jus a few lines you will be able to handle delays and not have to worry about handlers and cancelling this. This would also save it a lot of time if you have to create multiple handlers.

This will create a subscriber that will invoke the onNext() of the intervalSubscriber when an observable that this subscriber is subscribed to emits something.

// Set up a subscriber once. Setting up the subscriber
private Subscriber<Long> intervalSubscriber = new Subscriber<Long> () {
    @Override
    public void onCompleted() {
        //Wrap up things as onCompleted is called once onNext() is over
    }
    @Override
    public void onError(Throwable e) {
        //Keep an eye open for this. If onCompleted is not called, it means onError has been called. Make sure to override this method
    }
    @Override
    public void onNext(Long aLong) {
        // aLong will be from 0 to 1000
        // Yuor code logic goes here

        // If you want to run this code just once, just add a counter and call onComplete when the counter runs the first time

    }
} 

Let's go with with creating the observable that will emit.

//Setting up the Observable. This will make runThisOnInterval observable emit every 5 seconds on Computation Threadpool created and managed by RxJava.

private Observable<Long> runThisOnInterval = Observable.interval(5000, TimeUnit.MILLISECONDS, Schedulers.computation());

Ok, so we are all set now. All we need to do now is to subscriber intervalSubscriber to runThisOnInterval observable so that the observable can start producing and the subscriber can consume.

Simple call to subscribe() will start the emissions and it's NOT done on the main thread which gives me a lot of flexibility.

runThisOnInterval.subscribe(intervalSubscriber);

Answer 3

The difference between AlarmManager and Handler is AlarmManager will run even when the device is on sleep mode but handler will not. Other point to be consider is AlarmManager will consume more battery because it will wake up CPU and other chips.

As I understand your question you have to do some background task even when device is in sleep mode you have to use AlarmManager. Just try to keep the duration as minimum possible so it won't drain battery. You can start your alarm as InExact() with REAL_TIME type alarm.

You can checkout following links for your reference.

AlarmManager

Best Practices to keep device wake up