JavaFx - 方法未定义

Question

我必须使用 JavaFX 创建一个程序，该程序创建一个带有球的 Pane 。有四个按钮可以使球向左、向右、向上或向下移动。我不明白为什么当我去定义每个方法(如所示的 .left() )时，上面的方法调用仍然是一个错误，告诉我它是未定义的。

主类:

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class MoveTheBall extends Application {
    @Override
    public void start(Stage primaryStage) {
        StackPane pane = new StackPane();
        Circle circle = new Circle(20);
        circle.setStroke(Color.BLACK);
        circle.setFill(Color.WHITE);
        pane.getChildren().add(circle);

        HBox hBox = new HBox();
        hBox.setSpacing(10);
        hBox.setAlignment(Pos.CENTER);
        Button btLeft = new Button("Left");
        Button btRight = new Button("Right");
        Button btUp = new Button("Up");
        Button btDown = new Button("Down");
        hBox.getChildren().add(btLeft);
        hBox.getChildren().add(btRight);
        hBox.getChildren().add(btUp);
        hBox.getChildren().add(btDown);

        BorderPane borderPane = new BorderPane();
        borderPane.setCenter(pane);
        borderPane.setBottom(hBox);
        BorderPane.setAlignment(hBox, Pos.CENTER);

        Scene scene = new Scene(borderPane, 300, 200);
        primaryStage.setTitle("Move The Ball");
        primaryStage.setScene(scene);
        primaryStage.show();

    }
}

按钮类:

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class ControlBall extends Application {
    private MoveTheBall moveTheBall = new MoveTheBall();

    @Override
    public void start(Stage primaryStage) {

        HBox hBox = new HBox();
        hBox.setSpacing(5);
        hBox.setAlignment(Pos.CENTER);
        Button btLeft = new Button("Left");
        Button btRight = new Button("Right");
        Button btUp = new Button("Up");
        Button btDown = new Button("Down");
        hBox.getChildren().add(btLeft);
        hBox.getChildren().add(btRight);
        hBox.getChildren().add(btUp);
        hBox.getChildren().add(btDown);

        btLeft.setOnAction(new LeftHandler());
        btRight.setOnAction(new RightHandler());
        btUp.setOnAction(new UpHandler());
        btDown.setOnAction(new DownHandler());

        BorderPane borderPane = new BorderPane();
        borderPane.setCenter(moveTheBall);
        borderPane.setBottom(hBox);
        BorderPane.setAlignment(hBox, Pos.CENTER);

        Scene scene = new Scene(borderPane, 200, 150);
        primaryStage.setTitle("Move The Ball");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    class LeftHandler implements EventHandler<ActionEvent> {
        @Override
        public void handle(ActionEvent e) {
            moveTheBall.left(); // error because no class yet
        }
    }

    class RightHandler implements EventHandler<ActionEvent> {
        @Override
        public void handle(ActionEvent e) {
            moveTheBall.right(); // error because no class yet
        }
    }

    class UpHandler implements EventHandler<ActionEvent> {
        @Override
        public void handle(ActionEvent e) {
            moveTheBall.up(); // error because no class yet
        }
    }

    class DownHandler implements EventHandler<ActionEvent> {
        @Override
        public void handle(ActionEvent e) {
            moveTheBall.down(); // error because no class yet
        }
    }
}

class moveTheBall extends StackPane {
    private Circle ball = new Circle(20);

    public moveTheBall() {
        getChildren().add(ball);
        ball.setStroke(Color.BLACK);
        ball.setFill(Color.WHITE);
    }

    public void left() {
        ball.setCenterX(-2.0);
        ball.setCenterY(-2.0);
    }
}   

线 borderPane.setCenter(moveTheBall);也给我带来了问题。 “BorderPane 类型中的 setCenter(Node) 方法不适用于参数 (MoveTheBall)”

Answer 1

我对 JavaFX 还很陌生，但我会在这里尽力而为。

我建议不要使用完全独立的类来控制球、移动球和处理每个按钮，而是考虑使用 lambda 表达式来简化代码并减少出错的空间。例如，您可以通过编写如下行来设置 btRight 按钮的功能:

btRight.setOnAction(e -> {
    //if the ball is inside the right limit
        //Move the ball to the right
});

您可以将这些表达式直接写入 start() 方法中，并避免定义内部类以及控件的单独类。

至于为什么会出现错误，我最好的猜测(正如我所说，我对此很陌生)是 moveTheBall() 是 MoveTheBall 类的构造函数，但它被作为方法调用。

希望这有帮助。