Triggering a toast from a listener

I'm using an external package defining a JunctionActor. The idea is that a JunctionActor can send JSON messages to a remote server via a method called sendMessage and receive messages via a listener calling onMessageReceived. In my implementation, the device receives every message it sends, thus calling onMessageReceived. Yet, in my code, I've included a ChatClient object in my activity class, which has to call the show_message method. show_message triggers a Toast. When I'm calling show_message from onJoin, there is no problem at all, but when it's called from onMessageReceived, nothing shows up, whereas my debugger tells me that the app indeed receives a message and that onMessageReceived is triggered. In the mean time, the call of show_message in the onJoin method actually works. And I can't see any difference between both of them. Do you have a solution ?

Thanks a lot

public class HelloWorldJunctionActivity extends Activity {
     onCreate(...){...} [...]
private class ChatClient extends JunctionActor {
      public ChatClient() {
      public void onActivityJoin() {
      public void onMessageReceived(MessageHeader header, JSONObject msg) { 
          try { 
        } catch (JSONException e) {
            // TODO Auto-generated catch block
void show_message(String message) {
        .makeText(HelloWorldJunctionActivity.this, message, Toast.LENGTH_SHORT)


I'm not sure how JunctionActor works, but is it possible that the onMessageReceived callback is invoked from a thread which is not the UI thread? If that's the case you might have to use a Handler, as explained in this post.

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