multithreading - JavaFx ProgressBar doesn't update

Question

I try to understand how to update a ProgressBar in a multithreaded environment. I'm doing something wrong here but I don't see what it is. This should simply fill up the bar every 3sec but it doesn't:

    Task<Void> task = new Task<Void>(){
        @Override
        public Void call(){
            for (int i = 1; i < 10; i++)    {
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(i);
                updateProgress(i , 10);
            }
        return null;                
        }
    };

    updProg = new ProgressBar();
    updProg.progressProperty().bind(task.progressProperty());

    Thread th = new Thread(task);
    th.setDaemon(true);
    th.start();

What am I missing?

Answer 1

Your sample works fine for me.

The sample fills the bar a little bit every 3 seconds, completely filling the bar in half a minute.

I just wrapped it in some scaffolding code to make it executable and it worked without change (java7u15, win7).

import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class ProgressTest extends Application {
  public static void main(String[] args) { Application.launch(args); }
  @Override public void start(Stage stage) {
    Task<Void> task = new Task<Void>() {
      @Override public Void call() {
        for (int i = 0; i < 10; i++) {
          try {
            Thread.sleep(100);
          } catch (InterruptedException e) {
            Thread.interrupted();
            break;
          }
          System.out.println(i + 1);
          updateProgress(i + 1, 10);
        }
        return null;
      }
    };

    ProgressBar updProg = new ProgressBar();
    updProg.progressProperty().bind(task.progressProperty());

    Thread th = new Thread(task);
    th.setDaemon(true);
    th.start();

    StackPane layout = new StackPane();
    layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 10;");
    layout.getChildren().add(updProg);

    stage.setScene(new Scene(layout));
    stage.show();
  }
}

---

Perhaps you have been using some early access version of Java 8 which had a bug in it (now fixed) around ProgressBar updates.

RT-29018 ProgressBar and ProgressIndicator disappear when progressProperty is updated