How to access main thread from worker thread in Java?

Question

Read many overkilled, overcomplicated solution here in SO, for such an easy question, how to access main thread from a worker thread, to execute some code on it.

In iOS dispatch_get_main_queue() method returns main thread. How in Java?

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0UL), ^{
    //do background thread stuff

    dispatch_async(dispatch_get_main_queue(), ^{
        //update UI
    });
});

Possible duplicate of [Running code in main thread from another thread](http://stackoverflow.com/questions/11123621/running-code-in-main-thread-from-another-thread) — Augusto, Sep 16 '16 at 22:24
Neither of the links in your question have anything to do with Android. — CommonsWare, Sep 16 '16 at 22:33

score 1 · Accepted Answer · edited May 23 '17 at 12:10

1

In Android you can't access the main thread (UI Thread) directly, but you can queue jobs on it, so you need to create a Handler and using that handler to post jobs (Runnable) on main thread.

Below is an example of how you can post on UI Thread using Handler

new android.os.Handler(Looper.getMainLooper()).post(new Runnable() {
      @Override
      public void run() {
        //Doing job here
      }
    })

and also as @CommonsWare mentioned in the comments, there is another ways to access UI thread:

if you have instance of any View you can use View.post(Runnable)
if you have instance of Activity, you can use Activity.runOnUiThread(Runnable)

Btw accessing main thread in Android is totally different than Java Desktop Apps

edited May 23 '17 at 12:10

Community

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answered Sep 16 '16 at 22:27

Mohammad Ersan

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You do not need to create a `Handler`, as `post()` is also available on any `View`, and typically you have access to one of those. – CommonsWare Sep 16 '16 at 22:32
thats one of other solutions – Mohammad Ersan Sep 16 '16 at 22:33
@CommonsWare his question is how to access main thread from worker thread, so I assumed he doesn't have access to any Views – Mohammad Ersan Sep 16 '16 at 22:34

score -1 · Answer 2 · answered Sep 16 '16 at 22:37

-1

Running your code on main thread from another:

runOnUiThread(new Runnable() {
        @Override
        public void run() {
           // Your code here
        }
});

Hope this helps

answered Sep 16 '16 at 22:37

Lucas Moretto

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Curious why the downvote? Explanation? This code works fine to change state of the UI in the `doInBackground()` method of an AsyncTask for example. Is this not the "proper" way? – ShadowGod Sep 16 '16 at 23:09

How to access main thread from worker thread in Java?

2 Answers2