runOnUiThread vs Looper.getMainLooper().post in Android

Question

Can anyone tell me if there\'s any difference between using runOnUiThread() versus Looper.getMainLooper().post() to execute a task on the UI thread in Android??

Abou

Answer 1

The following behaves the same when called from background threads:

• using Looper.getMainLooper()

  Runnable task = getTask();
  new Handler(Looper.getMainLooper()).post(task);
  

• using Activity#runOnUiThread()

  Runnable task = getTask();
  runOnUiThread(task);
  

The only difference is when you do that from the UI thread since

public final void runOnUiThread(Runnable action) {
    if (Thread.currentThread() != mUiThread) {
        mHandler.post(action);
    } else {
        action.run();
    }
}

will check if the current Thread is already the UI thread and then execute it directly. Posting it as a message will delay the execution until you return from the current UI-thread method.

There is also a third way to execute a Runnable on the UI thread which would be View#post(Runnable) - this one will always post the message even when called from the UI thread. That is useful since that will ensure that the View has been properly constructed and has a layout before the code is executed.