Question

I have an application that has a GUI and TCP server. The TCP server is running in a different thread and when it receives a certain packet, it should start playing a video file (from MediaPlayer object). The problem is that as a GUI component, the video may be displayed only if invoked from the main thread. I added a listener class to the main class:

Class RequestListener implements NBRequestListener{  /* NBRequestListener is the interface */
public void onRequestArrived(String request) {
processRequest(request); /* This method will run the video */
}

I created a listener in the main thread and set it as a listener in the server:

RequestListener listener = new RequestListener();
server.setRequestListener(listener);

The code in the server is:

public void setRequestListener(_listener) {
listener = _listener; } /* listener is defined as RequestListener */

and the invocation of the event (in the server) is simply:

listener.onRequestArrived(input_from_client);

But the listener method is invoked in the server thread and not in the main thread and therefore I get exception: java.lang.reflect.InvocationTargetException. Could you please help pointing the problem?

Answer 1

Multiple ways to solve this one, here’s two:

1. Use a Handler in your Activity. For example, when you get a notification from your background thread, that the video needs to be played, you send a message to your Activity’s handler. Code in your custom Handler gets to run on the UI thread. Here’s a tutorial (from the many) http://www.helloandroid.com/taxonomy/term/43

2. When the background thread gets the packet, broadcast an Intent (startBroadcast() on the context class). Register a receiver for this broadcast in your Activity.