CRAM CRAM - 4 months ago 91
Android Question

Waiting for asynchronous callback in Android's IntentService

I have an

IntentService
that starts an asynchronous task in another class and should then be waiting for the result.

The problem is that the
IntentService
will finish as soon as the
onHandleIntent(...)
method has finished running, right?

That means, normally, the
IntentService
will immediately shut down after starting the asynchronous task and will not be there anymore to receive the results.

public class MyIntentService extends IntentService implements MyCallback {

public MyIntentService() {
super("MyIntentService");
}

@Override
protected final void onHandleIntent(Intent intent) {
MyOtherClass.runAsynchronousTask(this);
}

}

public interface MyCallback {

public void onReceiveResults(Object object);

}

public class MyOtherClass {

public void runAsynchronousTask(MyCallback callback) {
new Thread() {
public void run() {
// do some long-running work
callback.onReceiveResults(...);
}
}.start();
}

}


How can I make the snippet above work? I've already tried putting
Thread.sleep(15000)
(arbitrary duration) in
onHandleIntent(...)
after starting the task. Itseems to work.

But it definitely doesn't seem to be clean solution. Maybe there are even some serious problems with that.

Any better solution?

Answer

Use the standard Service class instead of IntentService, start your asynchronous task from the onStartCommand() callback, and destroy the Service when you receive the completion callback.

The issue with that would be to correctly handle the destruction of the Service in the case of concurrently running tasks as a result of the Service being started again while it was already running. If you need to handle this case, then you might need to set up a running counter or a set of callbacks, and destroy the Service only when they are all completed.