Call Main thread from secondary thread in Android

Question

How to call Main thread from secondary thread in Android?

Answer 1

The simplest way is to call runOnUiThread(...) from your thread

activity.runOnUiThread(new Runnable() {     public void run() {         ... do your GUI stuff     } }); 

Answer 2

My recommendation to communicate threads in the same process is sending messages between those threads. It is very easy to manage this situation using Handlers:

http://developer.android.com/reference/android/os/Handler.html

Example of use, from Android documentation, to handling expensive work out of the ui thread:

public class MyActivity extends Activity {      [ . . . ]     // Need handler for callbacks to the UI thread     final Handler mHandler = new Handler();      // Create runnable for posting     final Runnable mUpdateResults = new Runnable() {         public void run() {             updateResultsInUi();         }     };      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);          [ . . . ]     }      protected void startLongRunningOperation() {          // Fire off a thread to do some work that we shouldn't do directly in the UI thread         Thread t = new Thread() {             public void run() {                 mResults = doSomethingExpensive();                 mHandler.post(mUpdateResults);             }         };         t.start();     }      private void updateResultsInUi() {          // Back in the UI thread -- update our UI elements based on the data in mResults         [ . . . ]     } }