JavaFx ProgressBar doesnt update

问题:

I try to understand how to update a ProgressBar in a multithreaded environment. Iam doing something wrong here but I dont see what it is. This should simply fill up the bar every 3sec but it doesnt:

            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?

回答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

回答2:

Are you using the latest JDK 8 Early-Access? If so, see this bug report I filed: http://javafx-jira.kenai.com/browse/RT-29018

Basically, in a recent release of the early-access build, they made some changes in the skins and css. This caused a hidden bug to be revealed in which child nodes which are dirtier than parent nodes but both need repainting in the same pulse, the parent's dirty level ends up overwriting the child nodes dirty level.

This causes the progress to not show, and in fact, for me the progressBar became entirely invisible, as soon as updateProgress was called from the task. They have a patch in place, I don't know when this will go through.

A work-around, either use jdk7 while waiting on the patch, or you can do what I did and apply this from the old css into your css stylesheet:

/*hack to get progress bar working. From: JDK7u17 jfxrt.jar!/com/sun/javafx/scene/control/skin/caspian/caspian.css */

/*******************************************************************************
 *                                                                             *
 * ProgressBar                                                                 *
 *                                                                             *
 ******************************************************************************/

.progress-bar {
    -fx-skin: "com.sun.javafx.scene.control.skin.ProgressBarSkin";
    -fx-background-color:
        -fx-box-border,
        linear-gradient(to bottom, derive(-fx-color,30%) 5%, derive(-fx-color,-17%));
    -fx-background-insets: 0, 1;
    -fx-indeterminate-bar-length: 60;
    -fx-indeterminate-bar-escape: true;
    -fx-indeterminate-bar-flip: true;
    -fx-indeterminate-bar-animation-time: 2;
    -fx-focus-traversable: true;
}

.progress-bar .bar {
    -fx-background-color:
        -fx-box-border,
        linear-gradient(to bottom, derive(-fx-accent,95%), derive(-fx-accent,10%)),
        linear-gradient(to bottom, derive(-fx-accent,38%), -fx-accent);
    -fx-background-insets: 0, 1, 2;
    -fx-padding: 0.416667em; /* 5 */
}

.progress-bar:indeterminate .bar {
    -fx-background-color: linear-gradient(to left, transparent, -fx-accent);
}

.progress-bar .track {
     -fx-background-color:
        -fx-box-border,
        linear-gradient(to bottom, derive(-fx-color,-15%), derive(-fx-color,2.2%) 20%, derive(-fx-color,60%));
    -fx-background-insets:  0, 1;
}

.progress-bar:disabled {
    -fx-opacity: 1.0
}

回答3:

If you defined updProg in the FXML file, then the problem could be the initialization here.

try to just remove this line:

updProg = new ProgressBar();

回答4:

 Timeline updateProgressBar = new Timeline(new KeyFrame(Duration.seconds(1), new EventHandler<ActionEvent>() {
                @Override
                public void handle(ActionEvent event) {
                      /*Where Seconds and TotalSeconds are counter and total
                      respectively, also put somewhere Seconds++ or 
                      however you want to update progress. This time line 
                      will reapit each second */
                      progressBar.setProgress(Seconds / TotalSeconds);
                }
    }));
    updateProgressBar.setCycleCount(Timeline.INDEFINITE);
    updateProgressBar.play();