Thread and UI (Application) "communication"

[L Purcell]

Here's the scenario: A "start" button is clicked which sets up a Service/Task which includes I/O with a device. A changeListener is started, and the "start" button handler ends. Eventually, the changeListener detects a "change" and does its thing with the I/O device. NOW my question: How do I "notify" the user that the "change" (event) has occurred? "Update message" doesn't do anything since the "start" button routine has ended. I know I'm missing something fundamental here, but I'm baffled. (This is my first foray into the Service/Task business...) (The code in all other respects works great.) Thanks! L (Here is the boiled-down code.)

public class TestPhServerv1Controller  {
    @FXML  private Button btnStart;
    USBDevice usbDevice;  //It's a Phidget.
    @FXML
    private void handleStartAction(ActionEvent event) {      
      //Set up Service:
        ThrService thrService = new ThrService(); 
        thrService.start();                    
        thrService.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
            @Override
            public void handle(WorkerStateEvent wse) {
                txaInfo.appendText("On Succeeded: " + 
                                    wse.getSource().getValue() + " \n");
                txaInfo.appendText("Message: " + 
                                wse.getSource().getMessage() + " \n");
            }
        });
    } //End of Start-button-handler.
//-----------------------------------------------------------------------
    public static class ThrService extends Service<String> {
        @Override
        protected Task createTask() {
            return new Task<String>() {
                @Override protected String call() throws Exception {
                    
                // Omitted: section which sets up a USB I/O device, usbDevice; works great.                   
					//Set up serverSocket, clientSocket, PrintWriter outPW, BufferedReader inBR
                    //Send msg to client; read response. All is well...
				//Set up change-listener using device jar:	
                    usb-device.addInputChangeListener(new InputChangeListenerImpl(usb-device,   
                                            outPW, inBR) );       //Start InputChgListener... !!!!!

					updateMessage("Waiting for an Alarm Signal...");
					return "Waiting for alarm signal...";
			   
				} //End Task Call definition.               
//-----------------------------------------------------------------------                
          //Implement InputChangeListener:
                class InputChangeListenerImpl implements InputChangeListener {

                    private final USBDevice usbDevice; 
                    private final PrintWriter outPW;
                    private final BufferedReader inBR;

                    public InputChangeListenerImpl(USBDevice usbDevice, 
                                    PrintWriter outPW, 
                                        BufferedReader inBR) {
                        this.usbDevice = usbDevice;
                        this.outPW = outPW;
                        this.inBR = inBR;
                    } 

                    @Override   
                    public void inputChanged(InputChangeEvent ice) {                        
                                outPW.println("Alarm!");                //Send to client.
                                String inputLine = inBR.readLine();		//Read response from client.
                    }  //End of inputChanged method                    
                } //End of inputChangeListener class                
            }; //End of Task definition.            
        } //End of CreateTask.        
    } //End of Thread/Service/Task Class.      
} //End of Controller Class.

[Ranganathan Kaliyur Mannar]

This is an interesting scenario. The usual examples for tasks have a blocking task happening within the Task and so updation of GUI can be done. But, in this case, you just register a callback handler. Actually, in this case, you may not need the task to just install the listener.
And from within the listener, You can wrap the UI update call in Platform.runLater()

[L Purcell]

Ranga, thanks for the reply. I decided to keep the service/task since the setup part (which I omitted to save space) may hang/block. However, I solved the "communication" problem by BINDING the text in a textArea with the messageProperty in the Task! Perhaps this has the same effect as you were suggesting (by different means)?? Anyway, it all appears to work now, and I'm off struggling with the Android client code... Thanks again! L

[Ranganathan Kaliyur Mannar]

Ok, I see where the task was needed. I am not sure about the binding, because, I have never tried it myself - that sounds interesting.