Android - How can Services run in background?

Question

To my understanding, on android, Services run on the UI thread. I'm a little confused as to how services can run in the background - Should that not block the UI thread? How come they can both be on the main thread and run in the background at the same time?

Answer 1

Services run on the main thread by default, but they run in the background from the user's perspective - there's no screen backing the Service .

If you want your service to execute on a background thread, either use a Service subclass and provide your own threading - via a new Thread , the Java Executor framework, RxJava , AsyncTask , or use an IntentService subclass for "one-shot" type of tasks.

Answer 2

You can easily organize execution in background by yourself. But, if you want to perform single continious job once, consider using IntentService - it will run in separate thread and then finish. On the other hand, ordinary Service ca run indefinitely and you can bind to it. There is a few ways you can organize background tasks - AsyncTask, separate Thread, and, the most powerfull and convenient way- use rxJava library

Here is a code how you can execute some operation in background thread and process results on main thread with rxJava:

String arg = "132";
        Observable.defer(() -> Observable.just(arg))
                // start operation on background thread from
                // thread pool
                .subscribeOn(Schedulers.computation())
                .map(arg -> {
                    // do you processing here
                    String result = "123";
                    return result;
                })
                // switch to main thread
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(v -> {
                    // process results
                    Log.i("My service", "result: " + v);
                }, error -> {
                    // handle error
                });

As you can see, this is very convenient way of managing background operation, but, more importaint, you can switch threads as task progresses.

Answer 3

Service is always run on UI Thread

But If you run a service in UI thread then UI will be blocked.

So within the help of Thread or Asynctask you can call a service via Sap-rate Thread so that UI will not be blocked