绑定属性无效

Question

我正在JavaFX上做一个非常简单的游戏。我有两个对象来代表玩家：

1. player - Player类的实例
2. playerObj -矩形类的实例，用于表示地图上的播放器

现在，我实现了玩家移动的基本功能，如goUp、goLeft等，这些都改变了player类中的属性X和Y(这些是DoubleProperty类型)。现在我想让玩家的X和Y属性的每一个变化都反映在playerObj中，所以我使用了属性绑定，如下所示：

 playerObj.yProperty().bind(player.yProperty());

但是，当我调用goUp()方法时，player对象中的"y属性“将更改，而playerObj对象中的"y属性”不会更改。所以：

    pane.setOnKeyPressed(e -> {
        switch(e.getCode()) {
            case UP:
                player.goUp();
                System.out.println("player Y property: "+player.yProperty().getValue());
                System.out.println("playerObj Y property: "+playerObj.yProperty().getValue());
                break;
        }
    });

将导致这个结果(在调用goUp()方法3次之后)：

player Y property: 245.0
playerObj Y property: 250.0
player Y property: 240.0
playerObj Y property: 250.0
player Y property: 235.0
playerObj Y property: 250.0

为什么当我将playerObj Y属性绑定到player Y属性时，它的Y属性也没有改变？

编辑:完整代码(删除不相关部分)

Player.java

public class Player {

    private DoubleProperty x;
    private DoubleProperty y;
    private Scene scene;

    public Player(Scene scene) {
        this(DEFAULT_NAME, DEFAULT_COLOR, scene);
    }

    public Player(String name, Color color, Scene scene) {
        this.name = new SimpleStringProperty(name);
        this.color = color;
        this.scene = scene;
    }

    public Rectangle drawPlayer() {
        Rectangle player = new Rectangle(getX(),getY(),SIZE_OF_PLAYER,SIZE_OF_PLAYER);
        player.setFill(color);
        return player;
    }

    public Player goUp() {
        if(getY() != 0 && getY() != scene.getHeight()) {
           setY(yProperty().subtract(5).getValue());
       }
    }


    public DoubleProperty xProperty() {
        return x;
    }

    public DoubleProperty yProperty() {
        return y;
    }

    public double getX() {
        return x.getValue();
    }

    public void setX(double x) {
        this.x = new SimpleDoubleProperty(x);
    }

    public double getY() {
        return y.getValue();
    }

    public void setY(double y) {
        this.y = new SimpleDoubleProperty(y);
    }
}

Game.java

public class Game extends Application {

    private Scene scene;
    private Player player;
    private Rectangle playerObj;
    private Pane pane;

    @Override
    public void start(Stage primaryStage) {
        pane = new Pane();
        scene = new Scene(pane,500,500);
        player = new Player(scene);

        player.setX(scene.getWidth() / 2);
        player.setY(scene.getHeight() / 2);
        playerObj = player.drawPlayer();
        pane.getChildren().add(playerObj);
        playerObj.yProperty().bind(player.yProperty());

        pane.setOnKeyPressed(e -> {
            switch(e.getCode()) {
                case LEFT:
                    player.goLeft();
                    break;
                case UP:
                    player.goUp();
                    System.out.println("player Y property: "+player.yProperty().getValue());
                    System.out.println("playerObj Y property: "+playerObj.yProperty().getValue());
                    break;
                case RIGHT:
                    player.goRight();
                    break;
                case DOWN:
                    player.goDown();
            }
        });

        pane.requestFocus();

        primaryStage.setScene(scene);
        primaryStage.setTitle("Game");
        primaryStage.setResizable(false);
        primaryStage.show();

    }

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

Answer 1

您的x和y属性在Player类中实现得不正确。

调用player.setY(...)时，您将创建一个新的DoubleProperty

public void setY(double y) {
    this.y = new SimpleDoubleProperty(y);
}

当然，这不是您的节点先前绑定到的属性。因此，它的值没有反映在节点中。

你需要

public void setY(double y) {
    this.y.set(y);
}

setX(...)也是如此。