CODEWITHSUNDEEP
javaandroidmultithreadinglistviewandroid-asynctask
Wayne Fulcher
Wayne Fulcher

Reputation: 881

How to make more than one Android AsyncTask run at the same time?

OK so I have an Android app which has a listview on a fragment being loaded on the mainactivity. The list view contains an imageview which is loaded with an image from the devices external storage via an adapter which in turn calls an AsyncTask object called BackgroundImageLoader. At this point if I run my app everything work great and the images show nearly instantaneously. To give more detail about that process.... On the listview's adapter's bindView method I call a method which invokes the following: 

BackgroundImageLoader loader = new BackgroundImageLoader(photoID, imageView); 
loader.execute();

Now after I got the above code working perfectly I wrote some logic to "purge old photos". This logic was put in an AsyncTask object named AutoPurgePhotos_Task. Basically I want to run the task once on startup of the app but I just want it to run in the background so as not to interfere with the UI. I have tried launching it from the tail-end of the Applications onCreate() method and I have tried launching it from the MainActivity's onCreate() method. The results are such that the purging logic runs and works perfectly. And while it is running in the background my UI seems to be working as well with EVERYTHING EXCEPT the BackgroundImageLoader AsyncTask. None of the photos will begin to show until the AutoPurge task completes. Even to prove it has nothing to do with what I am doing in the task, I commented out all of my business logic and just have the task sleeping.

public class AutoPurgePhotos_Task  extends AsyncTask<Void, Void, Void> {

public AutoPurgePhotos_Task() {
    super();
}

@Override
protected Void doInBackground(Void... params) {

    SystemClock.sleep(10000);
    return null ;
}
}

As a side note I have other asynctask in my app that will not run either until this initial asynctask finishes. Its as if only one asynctask will run at a time. Again all other code that is in my UI thread appears to be running and working just fine while the asynctask is running. It just seems that only one asynctask will run at a time.

Here is how I launch the autopurge task...

AutoPurgePhotos_Task task = new AutoPurgePhotos_Task();
task.execute();

again I have tried launching it from several different areas and no matter where/how I launch it the other asynctask will wait till that one is done before they will run. Thanks for any help you can give me.

Upvotes: 0

Views: 700

Answers (1)

CommonsWare
CommonsWare

Reputation: 1007554

Use executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR) instead of execute(). Quoting the AsyncTask documentation:

If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.

Upvotes: 3

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