java - 绑定(bind)属性不起作用

Question

我正在使用 JavaFX 开发一个非常简单的游戏。我有两个代表玩家的对象:

1. player - Player 类的实例

2. playerObj - Rectangle 类的实例，用于表示 map 上的玩家

现在我实现了玩家移动的基本功能，如 goUp、goLeft 等。这些都更改了玩家类中的属性 X 和 Y(这些是 DoubleProperty 类型)。现在我想让玩家的 X 和 Y 属性的每次更改都会反射(reflect)在playerObj 中，因此我使用了如下属性绑定(bind):

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

但是当我调用 goUp() 方法时，player 对象中的“y 属性”将会更改，但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;
        }
    });

将导致以下结果(调用 goUp() 方法 3 次后):

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属性与player Y属性绑定(bind)时，它也没有改变？

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);
    }
}

游戏.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

Player 类中的 x 和 y 属性未正确实现。

当你调用player.setY(...)时，你创建了一个新DoubleProperty:

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

当然，这不是您的节点之前绑定(bind)的属性。所以它的值(value)并没有体现在节点上。

你需要

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

对于 setX(...) 也类似。