JavaFX：为什么 KeyEvent 不返回方法外的数据

Question

我对编程比较陌生，而且我很挣扎。我将非常非常感谢您的帮助。我正在尝试制作一个简单的程序，用户可以使用键盘上的数字 1 和 2 键更改透明舞台上显示的点的 Y 坐标，以上下移动它。问题是我在方法之外创建的 Y 值变量在按下键时不会更新。我知道实际的方法本身是有效的，因为我运行了打印线测试......除了该方法之外，我无法获得要在其他任何地方更新的值。有什么建议吗？

package application;

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.AnchorPane;
import javafx.scene.paint.Color;
import javafx.scene.text.Font;
import javafx.scene.text.Text;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

        //Program where the user can adjust the Y Coordinate of a dot by 
                     pressing 1 & 2 Keyboard Keys 

public class Main extends Application implements EventHandler<KeyEvent>  {


    double x = 680; //The X Value of Dot (Never Changes)
    double y = 380; //The Y Value of Dot (The value users can change)

    @Override
    public void start(Stage stage) {                                        

                    //Root Properties
        AnchorPane root = new AnchorPane(); 
        root.getChildren().addAll(dot(), display());            
        root.setStyle("-fx-background-color: null;");    

                    //Scene Properties

        Scene scene = new Scene(root,1369, 715);         
        scene.setOnKeyPressed(this);
        scene.setFill(null);    

                    //Stage Settings
        stage.initStyle(StageStyle.TRANSPARENT);           
        stage.setScene(scene);                          
        stage.show();
        stage.setAlwaysOnTop(true);

    }

    @Override
    //KeyEvent That Adjusts the Y Coordinate that Starts off at 380
    public void handle (KeyEvent event){

            KeyCode key = event.getCode();

            if (key == KeyCode.DIGIT1){y = y + 100;}
            if (key == KeyCode.DIGIT2){y = y - 100;}
            System.out.println(y); 
            //A test to see if the method actually works (it does)
            };


                    //Properties of the Dot
     public Text dot(){
         Text dot = new Text();
            dot.setText(".");
            dot.setFont(new Font (100));                
            dot.setFill(Color.RED);                 
            dot.setX(x);
            dot.setY(y);
            return dot;}

                    //Displays the Value of Y on the Screen
     public Text display(){
         Text display = new Text(Double.toString(y));
         display.setX(600);
         display.setY(300);

        return display;}

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

}

Answer 1

除了x, y 坐标之外，您还需要将dot 作为一个类字段。然后你就可以通过handle() 方法访问它并改变它的位置：

public class Main extends Application implements EventHandler<KeyEvent> {

    Text dot;

    double x = 680; //The X Value of Dot (Never Changes)
    double y = 380; //The Y Value of Dot (The value users can change)

    @Override
    public void start(Stage stage) {

        //Root Properties
        AnchorPane root = new AnchorPane();
        dot = dot();
        root.getChildren().addAll(dot, display());
        root.setStyle("-fx-background-color: null;");

        //Scene Properties

        Scene scene = new Scene(root,1369, 715);
        scene.setOnKeyPressed(this);
        scene.setFill(null);

        //Stage Settings
        stage.initStyle(StageStyle.TRANSPARENT);
        stage.setScene(scene);
        stage.show();
        stage.setAlwaysOnTop(true);

    }

    @Override
    //KeyEvent That Adjusts the Y Coordinate that Starts off at 380
    public void handle (KeyEvent event){

        KeyCode key = event.getCode();

        if (key == KeyCode.DIGIT1){dot.setY(dot.getY() + 100);}
        if (key == KeyCode.DIGIT2){dot.setY(dot.getY() - 100);}
        System.out.println(y);
        //A test to see if the method actually works (it does)
    };


    //Properties of the Dot
    public Text dot(){
        Text dot = new Text();
        dot.setText(".");
        dot.setFont(new Font(100));
        dot.setFill(Color.RED);
        dot.setX(x);
        dot.setY(y);
        return dot;}

    //Displays the Value of Y on the Screen
    public Text display(){
        Text display = new Text(Double.toString(y));
        display.setX(600);
        display.setY(300);

        return display;}

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

}