JavaFX PathTransition动画无法播放

Question

I have some code which is supposed to animate a circle along the path of an arc:

package event_handling;

import javafx.animation.PathTransition;
import javafx.animation.PathTransition.OrientationType;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Arc;
import javafx.scene.shape.ArcType;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
import javafx.util.Duration;

public class PalindromeSwing extends Application {

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

@Override
public void start(Stage primaryStage) throws Exception {

    Pane pane = new Pane();

    System.out.println(pane.getWidth());

    Arc a = new Arc(100, 100, 100, 100, -135, 90);
    a.setType(ArcType.OPEN);
    a.setStroke(Color.BLACK);
    a.setFill(Color.TRANSPARENT);

    Circle c = new Circle(5);

    pane.getChildren().addAll(a, c);

    PathTransition pt = new PathTransition();

    pt.setDuration(Duration.INDEFINITE);
    pt.setNode(c);
    pt.setPath(a);
    pt.setOrientation(OrientationType.ORTHOGONAL_TO_TANGENT);
    pt.setCycleCount(Timeline.INDEFINITE);
    pt.setAutoReverse(true);
    pt.play();

    Scene scene = new Scene(pane, 400, 400);

    primaryStage.setTitle("Animated circle");
    primaryStage.setScene(scene);
    primaryStage.show();

 }

}

However, when I run the program, no animation takes place. The circle appears at the beginning of the arc, and nothing happens:

Please help me understand why.

Answer 1

You have to set a definite duration for your animation, eg

pt.setDuration(Duration.seconds(4));

This value determines the duration of one animation cycle.

Duration.INDEFINITE is defined as Duration(Double.POSITIVE_INFINITY) . Using it will make the animation play with infinite duration, causing the interpolation steps to become too small to have an effect on the animated node.