Return a value after JavaFX Timeline has finished

user_3776738 0
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I'm using a timeline in JavaFX to do a countdown of a Label:

timeline.setCycleCount(6);
timeline.play();

And I want to return a value after the timeline has finished:

return true;

However, it seems that the value is getting returned immediately and the timeline runs parallel. How can I wait until the timeline has finished its countdown and then return the value without blocking the timeline?

EDIT:

To make it more clear, I already tried:

new Thread(() -> {
    timeline.play();
}).start();

while(!finished){ // finished is set to true, when the countdown is <=0

}
return true;

(This solution doesn't update the countdown.)

EDIT 2:

Here is a minimal, complete and verifiable example:

import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.Duration;


public class CountdownTest extends Application {

    private Label CountdownLabel;
    private int Ctime;

    @Override
    public void start(Stage primaryStage) {

        CountdownLabel=new Label(Ctime+"");

        StackPane root = new StackPane();
        root.getChildren().add(CountdownLabel);

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Countdown Test");
        primaryStage.setScene(scene);
        primaryStage.show();

        Ctime=5;

        if(myCountdown()){
            CountdownLabel.setText("COUNTDOWN FINISHED");
        }
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }

    public boolean myCountdown(){
         final Timeline timeline = new Timeline(
                            new KeyFrame(
                                    Duration.millis(1000),
                                    event -> {
                                    CountdownLabel.setText(Ctime+"");
                                    Ctime--;

                                    }

                            )
                    );
         timeline.setCycleCount(6);
         timeline.play();
    return true;
    }

}

You can see that it first shows "COUNTDOWN FINISHED" and counts down to 0 instead of starting with the countdown and counting down to "COUNTDOWN FINISHED".

javafx timeline java
4 Answers

As a Timeline inherits from Animation, you can use setOnFinished to define an action to occur at the end of the timeline.

timeline.setCycleCount(6);
timeline.play();
timeline.setOnFinished(event -> countdownLabel.setText("COUNTDOWN FINISHED"));
user_12477810

If you really want to wait till the timeline finished, you can use a CountDownLatch or a Semaphore along with setOnFinished. Something like the following should work:

CountDownLatch latch = new CountDownLatch(1);
timeline.setCycleCount(6);
timeline.setOnFinished(event -> latch.countDown());
timeline.play();
latch.await();
return true;
user_6003790

You are trying to wait in the one thread for the result of the work in the another thread. That is what synchronisation was created for! E.g. java.util.concurrent.Semaphore:

public boolean waitForTimeline()  {
    Semaphore semaphore = new Semaphore(0);

    System.out.println("starting timeline");
    Timeline t = new Timeline();
    t.getKeyFrames().add(new KeyFrame(Duration.seconds(2)));
    t.setOnFinished((e)-> {
        System.out.println("releasing semaphore"); 
        semaphore.release();
    });
    t.play();

    System.out.println("waiting for timeline to end");
    try {
        semaphore.acquire();
    } catch (InterruptedException ex) {
        ex.printStackTrace();
        return false;
    }
    return true;
}

But note, that you can't run this method on "JavaFX Application Thread" as it will block UI updates. Run it on a separate thread:

new Thread(()-> { 
    System.out.println("returned from timeline with " + waitForTimeline()); 
}).start();

or, better, instead create a listener with the logic you do after return and call that listener from t.setOnFinished(). For your example, it will be:

public void myCountdown(Runnable onSuccess){
    //...
    timeline.setOnFinished((e)-> {
        onSuccess.run();
    });
}

and corresponding call:

myCountdown(()->{
    CountdownLabel.setText("COUNTDOWN FINISHED");
});
user_10541400

Use Animation's setOnFinished in addition to the KeyFrame's setOnFinished that you have (a Timeline is an Animation). Iv'e modified your MCVE to show how to do that for your case:

public class CountdownTest extends Application {

    private Label countdownLabel;
    private int ctime = 5;

    @Override
    public void start(Stage primaryStage) {
        countdownLabel = new Label();

        StackPane root = new StackPane();
        root.getChildren().add(countdownLabel);

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Countdown Test");
        primaryStage.setScene(scene);
        primaryStage.show();

        myCountdown();
    }

    public void myCountdown() {
        final Timeline timeline = new Timeline(new KeyFrame(Duration.millis(1000),
            event -> {
                countdownLabel.setText(ctime + "");
                ctime--;
            }
        ));
        timeline.setCycleCount(ctime + 1);
        timeline.setOnFinished(e -> countdownLabel.setText("COUNTDOWN FINISHED"));
        timeline.play();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

On each cycle, the KeyFrame's setOnFinished will be executed, reducing the count by 1. When the whole animation finishes (all of its cycles), the Timeline's setOnFinished will be executed.

Notes:

  • Use the ctime variable to calculate the number of cycles so that they match.
  • Use the Java naming conventions: identifiers (names) start with lowercase.
  • Indent your code properly so that it's easier to read.
user_18035510
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