runOnUiThread vs Looper.getMainLooper().post in Android

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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.

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