Android basics running code in the UI thread

Question

In the viewpoint of running code in the UI thread  is there any difference between   MainActivity this runOnUiThread new Runnable         public void run             Log d  UI thread    I am the UI thread                or  MainActivity this myView post new Runnable         public void run             Log d  UI thread    I am the UI thread                and  private class BackgroundTask extends AsyncTask lt String  Void  Bitmap gt        protected void onPostExecute Bitmap result            Log d  UI thread    I am the UI thread

User · Answer

There is a fourth way using Handler  new Handler   post new Runnable          Override     public void run                Code here will run in UI thread

User · Answer

None of those are precisely the same  though they will all have the same net effect   The difference between the first and the second is that if you happen to be on the main application thread when executing the code  the first one  runOnUiThread    will execute the Runnable immediately  The second one  post    always puts the Runnable at the end of the event queue  even if you are already on the main application thread   The third one  assuming you create and execute an instance of BackgroundTask  will waste a lot of time grabbing a thread out of the thread pool  to execute a default no-op doInBackground    before eventually doing what amounts to a post    This is by far the least efficient of the three  Use AsyncTask if you actually have work to do in a background thread  not just for the use of onPostExecute

User · Answer

As of Android P you can use getMainExecutor     getMainExecutor   execute new Runnable        Override public void run            Code will run on the main thread           From the Android developer docs      Return an Executor that will run enqueued tasks on the main thread associated with this context  This is the thread used to dispatch calls to application components  activities  services  etc     From the CommonsBlog      You can call getMainExecutor   on Context to get an Executor that will execute its jobs on the main application thread  There are other ways of accomplishing this  using Looper and a custom Executor implementation  but this is simpler

User · Answer

The answer by Pomber is acceptable  however I m not a big fan of creating new objects repeatedly  The best solutions are always the ones that try to mitigate memory hog  Yes  there is auto garbage collection but memory conservation in a mobile device falls within the confines of best practice  The code below updates a TextView in a service    TextViewUpdater textViewUpdater   new TextViewUpdater    Handler textViewUpdaterHandler   new Handler Looper getMainLooper     private class TextViewUpdater implements Runnable      private String txt       Override     public void run             searchResultTextView setText txt             public void setText String txt           this txt   txt             It can be used from anywhere like this   textViewUpdater setText  Hello            textViewUpdaterHandler post textViewUpdater

User · Answer

If you need to use in Fragment you should use   private Context context        Override     public void onAttach Context context            super onAttach context           this context   context                MainActivity context  runOnUiThread new Runnable             public void run                 Log d  UI thread    I am the UI thread                        instead of  getActivity   runOnUiThread new Runnable         public void run             Log d  UI thread    I am the UI thread                Because There will be null pointer exception in some situation like pager fragment

User · Answer

use Handler new Handler Looper getMainLooper    post new Runnable          Override     public void run                Code here will run in UI thread

User · Answer

I like the one from HPP comment  it can be used anywhere without any parameter   new Handler Looper getMainLooper    post new Runnable          Override     public void run             Log d  UI thread    I am the UI thread

[android] Android basics: running code in the UI thread

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