Trying to update UI with from another thread

Question

Hi,
I start a JavaFX application from another class, and then I want to modify UI components from it. I have been trying to use Platform.runLater to do it.
But the GUI hangs initially (doesnt display anything) for the first 5 seconds (sleep time) and then modifies and shows it.
I want to display the GUI at first, and then after 5 seconds the GUI should update with the message, but with the below code it just hangs first and displays everything after 5seconds.
Here sampleGUI is a a javafx app with text fields in it.
+public class StartGame extends Application {+
+@Override+
+public void start(Stage stage) throws Exception {+
final sampleGUI gui = new sampeGUI();
gui.start(stage);
+Platform.runLater(new Runnable() {+
+@Override+
+public void run() {+
+try {+
System.out.println("Sleeping now...");
Thread.sleep(5000);
System.out.println("Sleep over!");
gui.updateText("New message");
+} catch (InterruptedException ex) {+
System.out.println("exception" ex);+
+}+
+}+
+});+
+}+
+}+

Answer 1

Platform.runLater(new Runnable() {
  @Override
  public void run() {
});causes the Runnable's run method to be executed on the FX Application Thread. Since you put Thread.sleep(5000) inside your Runnable's run method, the sleep happens on the FX Application Thread.
The call to runLater(...) can be invoked from any thread, including the FX Application Thread.
So if you are not in the FX Application thread, you want to do:
// any long-running task, for example
System.out.println("Sleeping now");
Thread.sleep(5000);
System.out.println("Sleep over");
Platform.runLater(new Runnable() {
  @Override
  public void run() {
    // update UI:
    gui.updateText("New Message");
});If you are on the FX Application thread, which is the case in your Application.start(...) method, you need to create a new thread to execute your long-running code. You can do this "by hand", creating a Thread and a Runnable for it to execute, but it's probably better to use the JavaFX concurrency API, which has lots of useful hooks for updating the UI on the FX Application Thread.
In this case, the code would look like this:
public class StartGame extends Application {
  @Override
  public void start(Stage stage) throws Exception {
    final SampleGUI gui = new SampleGUI();
    gui.start();
    final Task<String> waitingTask = new Task<String>() {
      @Override
      public String call() throws Exception {
        System.out.println("Sleeping");
        Thread.sleep(5000);
        System.out.println("Sleep over!");
        return "New Message" ;
    waitingTask.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
      @Override
      public void handle(WorkerStateEvent event) {
        gui.updateMessage(waitingTask.getValue());
    ExecutorService executor = Executors.newSingleThreadExecutor();
    executor.submit(waitingTask);
}There are (probably dozens of) other ways to use a Task to do this. See the [url http://docs.oracle.com/javafx/2/api/javafx/concurrent/Task.html]API docs for Task for more.