java - 单击按钮后弹出异常(java fx)

Question

我正在制作一个应用程序，您可以选择绘制矩形或直线，并且还可以选择清除 Canvas 。清除 Canvas 按钮可以工作，但每次单击清除 Canvas 按钮时都会显示一堆异常。我只是想通过尝试确定它的含义来消除异常

我已经尝试仔细检查代码中的错误(任何语法或逻辑错误)，但我仍然没有指出问题所在。我是一个相当新的程序员，所以我可能没有足够的知识来尝试找到它，我也要求其他人看一下，他们说一切似乎都很好。

以下是单击一键后的错误总数 ( /image/JYkNt.jpg )。

这是 GitHub 上的代码 ( https://github.com/DWER-afk/DWERR.git )

感谢所有帮助，并提前感谢您查看它。(刚刚添加的代码块和 Line、Main 和矩形都是单独的类)

`import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.control.*;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import org.w3c.dom.css.Rect;

import java.util.ArrayList;



public class Main extends Application {

    // Layout sizes
    int a = 0;
    final double SCREEN_WIDTH = 1000;
    final double SCREEN_HEIGHT = 800;
    final double CONTROL_HEIGHT = -175;
    private GraphicsContext gc, transgc;
    private double sx, sy;
    private double ex, ey;
    private Color lineColor = Color.BLUE;
    private ColorPicker lineColorPicker;
    private TextField tf;
    public double lines123 = 1.0;

    // Reference to the Model
    private ArrayList<Rectangle> rectangle1;
    private ArrayList<Line> lines;
    // TODO: Private Event Handlers and Helper Methods

    private void pressHandler(MouseEvent me) {
        sx = me.getX();
        sy = me.getY();
    }

    private void releaseHandler(MouseEvent me) {
        ex = me.getX();
        ey = me.getY();
        if(a == 0){Line l = new Line(sx,sy,ex,ey,lineColorPicker.getValue(),lines123);
            lines.add(l);
            for (Line l1 : lines)
                l1.draw(gc);
            transgc.clearRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);}
        if(a == 1){Rectangle rl = new Rectangle(sx,sy,ex,ey,lineColorPicker.getValue(),lines123);
            rectangle1.add(rl);

            for (Rectangle r1 : rectangle1)
                r1.draw(gc);
            transgc.clearRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);}



    }


    /**
     * This will draw a "Rubberband" line on the transparent surface above the drawing.
     *
     * @param me The mouse drag event - not used in method
     */
    private void dragHandler(MouseEvent me) {
        transgc.clearRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
        ex = me.getX();
        ey = me.getY();
        if(a == 0){
            Line tempLine = new Line(sx,sy,ex,ey,lineColorPicker.getValue(),lines123);
            tempLine.draw(transgc);
        }
        if (a == 1){
            Rectangle temprect = new Rectangle(sx,sy,ex,ey,lineColorPicker.getValue(),lines123);
            temprect.draw(transgc);
        }

    }

    /**
     * This is where you create your components and the model and add event
     * handlers.
     *
     * @param stage The main stage
     * @throws Exception
     */
    @Override
    public void start(Stage stage) throws Exception {
        Pane root = new Pane();
        Scene scene = new Scene(root, SCREEN_WIDTH, SCREEN_HEIGHT, Color.DARKGRAY); // set the size here
        stage.setTitle("Java Shape Drawer by Alexei Ougriniouk"); // set the window title here
        stage.setScene(scene);
        // TODO: Add your GUI-building code here

        // 1. Create the model - No model yet

        lines = new ArrayList<>();
        rectangle1 = new ArrayList<>();
        // 2. Create the GUI components - Just a CANVAS for now

        Canvas c = new Canvas(SCREEN_WIDTH, SCREEN_HEIGHT - CONTROL_HEIGHT);
        c.relocate(0, CONTROL_HEIGHT);
        Canvas transc = new Canvas(SCREEN_WIDTH, SCREEN_HEIGHT);
        transc.relocate(0, CONTROL_HEIGHT);

        // Add JavaFX controls to top pane ...

        Label colorLabel = new Label("Change line Colours");
        colorLabel.relocate(100, 625);

        lineColorPicker = new ColorPicker(lineColor);
        lineColorPicker.relocate(100, 650);

        Button resetButton = new Button("Reset Shape Colors");
        resetButton.relocate(100,750);
        resetButton.setOnAction(this::resetHandler);

        Button clearstuff =  new Button("Clear Canvas");
        clearstuff.relocate(450,675);
        clearstuff.setOnAction(this::clearHandler);

        Button linedraw =  new Button("line");
        linedraw.relocate(350,635);
        linedraw.setDefaultButton(true);
        linedraw.setOnAction(this::lineHandler);

        Button rectdraw =  new Button("rectangle");
        rectdraw.relocate(450,635);
        rectdraw.setOnAction(this::rectHandler);

        tf = new TextField("1");
        tf.relocate(250,750);

        // 3. Add components to the root
        root.getChildren().addAll(c, transc, colorLabel, lineColorPicker, resetButton, tf,clearstuff,linedraw,rectdraw);

        // Create the two graphics contexts

        gc = c.getGraphicsContext2D();
        transgc = transc.getGraphicsContext2D();

        gc.setFill(Color.WHITE);
        gc.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
        // 5. Add Event Handlers and do final setup
        transc.addEventHandler(MouseEvent.MOUSE_PRESSED, this::pressHandler);
        transc.addEventHandler(MouseEvent.MOUSE_RELEASED, this::releaseHandler);
        transc.addEventHandler(MouseEvent.MOUSE_DRAGGED, this::dragHandler);
        // 6. Show the stage
        stage.show();
    }
    private void clearHandler(ActionEvent actionEvent){
        gc.clearRect(0,0,SCREEN_WIDTH,SCREEN_HEIGHT);
        for(Line l : lines) {
            l.setLineColor(lineColorPicker.getValue());
            lines.clear();
        }
        for(Rectangle rl : rectangle1 ) {
            rl.setLineColor(lineColorPicker.getValue());
            rectangle1.clear();
        }

    }


    private void resetHandler(ActionEvent actionEvent) {
        for(Line l : lines) {
            l.setLineColor(lineColorPicker.getValue());
            l.draw(gc);
        }
        for(Rectangle l : rectangle1) {
            l.setLineColor(lineColorPicker.getValue());
            l.draw(gc);
        }



        try {
            int lineWidth = Integer.parseInt(tf.getText());
            if(lineWidth > 0){
                new Alert(Alert.AlertType.INFORMATION,
                        "VALUE APPROVED : Value in TextBox = " + String.valueOf(lineWidth)).showAndWait() ;
                lines123 = (double) lineWidth;
            }
            if(lineWidth <= 0){
                new Alert(Alert.AlertType.ERROR,
                        "Could not convert " + tf.getText() + " to an integer due to it being negative").showAndWait();
            }

        }
        catch (NumberFormatException ex)
        {
            new Alert(Alert.AlertType.ERROR,
                    "Could not convert " + tf.getText() + " to an integer").showAndWait();

        }

    }
    private void lineHandler(ActionEvent actionEvent) {
        a = 0;
        if(a == 0){for(Line l : lines) {
            l.setLineColor(lineColorPicker.getValue());
            l.draw(gc);
        }}


    }
    private void rectHandler(ActionEvent actionEvent) {
        a = 1;
        if(a == 1){for(Rectangle l : rectangle1) {
            l.setLineColor(lineColorPicker.getValue());
            l.draw(gc);
        }}
    }

    /**
     * Make no changes here.
     * @param args unused
     */
    public static void main(String[] args) {
        launch(args);
    }
}
'

这是 Line 类

public class Line {
    Main sc = new Main();
    private double sx, sy, ex, ey;
    private Color lineColor;
    double lineswidth = sc.lines123;
    public Line(double sx, double sy, double ex, double ey, Color lineColor, double lineswidth)
    {
        this.sx = sx;
        this.sy = sy;
        this.ex = ex;
        this.ey = ey;
        this.lineColor = lineColor;
        this.lineswidth = lineswidth;
    }

    /**
     * Draw a rectangle to the Graphics context
     * @param gc the graphics context of the FX component
     */
    public void draw(GraphicsContext gc) {
        gc.setStroke(lineColor);
        gc.setLineWidth(lineswidth);
        // For circle drawing must get the smaller of the two X values, same for Y
        gc.strokeLine (sx,sy,ex,ey);
    }

    public void setLineColor(Color newColor)
    {
        lineColor = newColor;
    }


    @Override
    public String toString() {
        return "Line{}" + super.toString();
    }

}

这是矩形类

import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;

public class Rectangle {
    Main sc = new Main();
    private double sx, sy, ex, ey;
    private Color lineColor;
    double lineswidth = sc.lines123;
    public Rectangle(double sx, double sy, double ex, double ey, Color lineColor, double lineswidth)
    {
        this.sx = sx;
        this.sy = sy;
        this.ex = ex;
        this.ey = ey;
        this.lineColor = lineColor;
        this.lineswidth = lineswidth;
    }

    /**
     * Draw a rectangle to the Graphics context
     * @param gc the graphics context of the FX component
     */
    public void draw(GraphicsContext gc) {
        {
            gc.setStroke(Color.BLACK);
            gc.strokeRect(sx,sy,ex,ey);
            gc.setLineWidth(lineswidth);
            // For circle drawing must get the smaller of the two X values, same for Y
            gc.setFill(lineColor);
            gc.fillRect(sx,sy,ex,ey);
        }

    }

    public void setLineColor(Color newColor)
    {
        lineColor = newColor;
    }


    @Override
    public String toString() {
        return "Line{}" + super.toString();
    }

}

Answer 1

在两个绘图函数中，在开始时执行以下操作:double sx = this.sx, sy = this.sy, ex = this.ex, ey = this.ey;

现在，绘制时变量无法更改。