Javafx在使用计时器时不在fx应用程序线程上

Question

我正在用这个

import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;



public class Main extends Application {

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

@Override
public void start(Stage primaryStage) {
    Group root = new Group();
    Scene scene = new Scene(root, 600, 400);
    primaryStage.setScene(scene);
    Circle circle = new Circle(300,200,50, Color.BLACK);
    primaryStage.setTitle("Circle");
    primaryStage.setResizable(false);
    root.getChildren().add(circle);
    moveCircle(circle, scene);
    primaryStage.show();
}
public int random(int min, int max) {
    return new Random().nextInt((max - min) + min);
}

public int random(int max) {
    return random(0, max);
}

public void moveCircle(Circle circle, Scene scene) {
    Platform.runLater(() -> {
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new TimerTask() {

            @Override
            public void run() {
                circle.setCenterX(random((int) scene.getX()));
                circle.setCenterY(random((int) scene.getY()));

            }
        }, 1000, 1000);
    });
}

但是这个：

public void moveCircle(Circle circle, Scene scene) {
    Platform.runLater(() -> {
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new TimerTask() {

            @Override
            public void run() {
                circle.setCenterX(random((int) scene.getX()));
                circle.setCenterY(random((int) scene.getY()));

            }
        }, 1000, 1000);
    });
}

给我这个错误：

Exception in thread "Timer-0" java.lang.IllegalStateException: Not on FX application thread; currentThread = Timer-0
    at com.sun.javafx.tk.Toolkit.checkFxUserThread(Toolkit.java:204)
    at com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:364)
    at javafx.scene.Scene.addToDirtyList(Scene.java:485)
    at javafx.scene.Node.addToSceneDirtyList(Node.java:424)
    at javafx.scene.Node.impl_markDirty(Node.java:415)
    at javafx.scene.shape.Shape.impl_markDirty(Shape.java:942)
    at javafx.scene.shape.Circle$1.invalidated(Circle.java:136)
    at javafx.beans.property.DoublePropertyBase.markInvalid(DoublePropertyBase.java:112)
    at javafx.beans.property.DoublePropertyBase.set(DoublePropertyBase.java:146)
    at javafx.scene.shape.Circle.setCenterX(Circle.java:122)
    at Main$2.run(Main.java:48)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

而且我真的不明白怎么了

Answer 1

可能是因为您误解了Platform.runLater()工作原理。

正确的代码段为：

public void moveCircle(Circle circle, Scene scene) {
    Timer timer = new Timer();
    timer.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            Platform.runLater(() -> {
                circle.setCenterX(random((int) scene.getX()));
                circle.setCenterY(random((int) scene.getY()));
            });
        }
    }, 1000, 1000);
}

但：

我强烈建议您不要使用Timer，TimeLine而是使用！它是JavaFX
API的一部分，您不必执行这些Platform.runLater()调用。这只是很快就被黑了，但是您知道了：

public void moveCircle(Circle circle, Scene scene) {
    Timeline timeline = new Timeline(new KeyFrame(Duration.seconds(1), ev -> {
        circle.setCenterX(random((int) scene.getX()));
        circle.setCenterY(random((int) scene.getY()));
    }));
    timeline.setCycleCount(Animation.INDEFINITE);
    timeline.play();
}