Dynamic adding of components (doesn't work when programmatically)

Question

Hi, I don't understand, why this doesn't work. I'll explain it on this example:
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class NewFXMain extends Application {
    Group root;
    public static void main(String[] args) {
        Application.launch(NewFXMain.class, args);
    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Hello World");
        root = new Group();
        Scene scene = new Scene(root, 300, 250, Color.LIGHTGREEN);
        Button btn = new Button();
        btn.setLayoutX(100);
        btn.setLayoutY(80);
        btn.setText("Add button now");
        btn.setOnAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent event) {
                addButton();
        root.getChildren().add(btn);  
        primaryStage.setScene(scene);
        primaryStage.setVisible(true);
        System.err.println("Number of buttons before: "+root.getChildren().size());
        ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
        executor.schedule(new MyTask(), 5, TimeUnit.SECONDS);
    private void addButton() {
        System.err.println("Button adding");
        root.getChildren().add(new Button("YEAH"));
        System.err.println("Number of buttons after: "+root.getChildren().size());
    class MyTask implements Runnable {
        public void run() {
            addButton();
}There are two ways how a new button can be added. Either by clicking on existing button or programmatically by the program itself after 5 seconds.
If you add it by button, there is no problem. The error print is:
Number of buttons before: 1
Button adding
Number of buttons after: 2
But if you just wait, then the error print is:
Number of buttons before: 1
Button adding
and no button is added. In fact, the error printing after the adding isn't performed either.
I'd like to ask if there is some solution for this because I'd love to do some changes by schedulers. Thx
Edited by: 876949 on 14.8.2011 9:09
Edited by: 876949 on 14.8.2011 9:11

Answer 1

No, these are not error messages, they are just for purpose of example. Here it doesn't matter whether err or out... (yes, 'out' would be better ;)
But thanx, it's working. By the way, I am creating scheduler for task lists. They are supposed to be printed dynamically in specific time (or periodically). For example: at 5 o'clock I need to print 5 items of some list and every 3 hours I need to print 3 items of another list etc. - so it's quite dynamic with regard to component adding (No, I don't want to use some sort of ListView, I want interactive printing: one item on screen at a moment). I'll try to work your solution into my code.
Edit: So either it's not possible to use this for the purpose of my app or it will be really cumbersome. Maybe it would be easier to draw some rectangles with mouse listeners...
Edit: So I finally got around it. In the end, I won't use dynamic adding as intended. It's working and that's important.
Edited by: 876949 on 14.8.2011 12:48
Edited by: 876949 on 15.8.2011 5:21