Java GUI Window 显示垃圾

Question

我编写了一个 Java 程序，根据用户执行的按钮点击操作，对三角形进行旋转、移动或旋转并移动。

事先，我指示用户输入逻辑坐标范围以确定像素坐标将如何映射到真实的 x-y 坐标系。

最初，我的三角形出现在屏幕中间，点击按钮后，三角形在其上进行了一定的操作（即旋转、移动等）后显示

但是，在操作完成并重新绘制三角形后，我看到在JPanel 的左上角也绘制了一个输入框。

我不确定这怎么一直画在那里。

代码：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class RotateAndShiftTriangles extends JFrame {
    public static void main(String[] args) { new RotateAndShiftTriangles(); }

   RotateAndShiftTriangles() {
       super("Drawing 50 Triangles");

       final JPanel drawingPanel = new DrawTriangles();
       JPanel buttonPanel = new JPanel();
       JButton rotate = new JButton("Rotate"),
               shift = new JButton("Shift"),
               rotateShift = new JButton("Rotate and Shift"),
               reset = new JButton ("Reset");

       drawingPanel.setBackground(Color.WHITE);

       buttonPanel.add(rotate);
       buttonPanel.add(shift);
       buttonPanel.add(rotateShift);
       buttonPanel.add(reset);

       addWindowListener(new WindowAdapter() {
           public void windowClosing(WindowEvent e) {
               System.exit(0);
           }
       });

       DrawTriangles.rWidth = Float.parseFloat(JOptionPane.showInputDialog("Input rWidth"));
       DrawTriangles.rHeight = Float.parseFloat(JOptionPane.showInputDialog("Input rHeight"));

       rotate.addActionListener(new ActionListener() {

           public void actionPerformed(ActionEvent e) {
               DrawTriangles.rotate = true;
               drawingPanel.repaint();
           }
       });

       shift.addActionListener(new ActionListener() {

           public void actionPerformed(ActionEvent e) {
               DrawTriangles.shift = true;
               drawingPanel.repaint();
           }
       });

       rotateShift.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {
                DrawTriangles.rotate = true;
                DrawTriangles.shift = true;
                drawingPanel.repaint();
            }
       });

       reset.addActionListener(new ActionListener() {

        @Override
            public void actionPerformed(ActionEvent e) {
                DrawTriangles.reset = true;
                drawingPanel.repaint();
            }
       });

       setSize(600, 400);
       add("South", buttonPanel);
       add("Center", drawingPanel);
       setVisible(true);
   }
}

class DrawTriangles extends JPanel {
    static float rWidth, rHeight, pixelSize;
    static int maxX, maxY, minMaxXY, centerX, centerY;
    static boolean rotate = false, shift = false, reset = false;
    float angle = 0;

    void initialize() {
        Dimension d = getSize();
        maxX = d.width - 1; maxY = d.height - 1;
        pixelSize = Math.max(rWidth / maxX, rHeight / maxY);
        minMaxXY = Math.min(maxX, maxY);
        centerX = maxX/2; centerY = maxY/2;
    }

    public int iX2(float x) { return Math.round(x); }
    public int iY2(float y) { return maxY - Math.round(y); }
    public static int iX(float x) { return Math.round(centerX + x / pixelSize); }
    public static int iY(float y) { return Math.round(centerY - y / pixelSize); }
    public static float fx(int x) { return (x - centerX) * pixelSize; }
    public static float fy(int y) { return (centerY - y) * pixelSize; }

    public void paint(Graphics g) {
        super.paintComponent(g);
        initialize();

        int left = iX(-rWidth/2), right = iX(rWidth/2);
        int top = iY(rHeight/2), bot = iY(-rHeight/2);

        g.drawString("X: " + -rWidth/2 + " Y: " + rHeight/2, left, top + 10);
        g.drawString("X: " + rWidth/2 + " Y: " + rHeight/2, right - 55, top + 10);
        g.drawString("X: " + -rWidth/2 + " Y: " + -rHeight/2, left, bot);
        g.drawString("X: " + rWidth/2 + " Y: " + -rHeight/2, right - 55, bot);

        g.setColor(Color.BLUE);
        g.drawRect(left, top, right - left, bot - top);

        float side = 0.95f * minMaxXY, sideHalf = 0.5F * side,
                h = sideHalf * (float)Math.sqrt(3),
                xA, yA, xB, yB, xC, yC, 
                xA1, yA1, xB1, yB1, xC1, yC1, p, q;

        q = 0.05F;
        p = 1 - q;

        xA = centerX - sideHalf;
        yA = centerY - 0.5F * h;
        xB = centerX + sideHalf;

        yB = yA;

        xC = centerX;
        yC = centerY + 0.5F * h;

        if(!reset) {
            if(rotate) {
                angle += Float.parseFloat(JOptionPane.showInputDialog("Input Angle of Rotation (in degrees)"));
                float xR = fx(Integer.parseInt(JOptionPane.showInputDialog("Input X Coordinate for Rotation"))),
                        yR = fx(Integer.parseInt(JOptionPane.showInputDialog("Input Y Coordinate for Rotation")));

                xA = rotateX(xA, yA, xR, yR, angle);
                yA = rotateY(xA, yA, xR, yR, angle);

                xB = rotateX(xB, yB, xR, yR, angle);
                yB = rotateY(xB, yB, xR, yR, angle);

                xC = rotateX(xC, yC, xR, yR, angle);
                yC = rotateY(xC, yC, xR, yR, angle);

                rotate = false;
            }
            if(shift) {
                float xShift = -fx(Integer.parseInt(JOptionPane.showInputDialog("Input X Coordinate for Shift"))),
                        yShift = -fx(Integer.parseInt(JOptionPane.showInputDialog("Input Y Coordinate for Shift")));

                xA += xShift; 
                yA += yShift;

                xB += xShift;
                yB += yShift;

                xC += xShift;
                yC += yShift;

                shift = false;
            }
        }

        g.setColor(Color.RED);
        for (int i = 0; i < 50; i++) {
            g.drawLine(iX2(xA), iY2(yA), iX2(xB), iY2(yB));
            g.drawLine(iX2(xB), iY2(yB), iX2(xC), iY2(yC));
            g.drawLine(iX2(xC), iY2(yC), iX2(xA), iY2(yA));

            if(i == 0) {
                g.setColor(Color.BLACK);
                g.drawString("A: X- " + xA + " Y- " + yA, 0, 50);
                g.drawString("B: X- " + xB + " Y- " + yB, 0, 60);
                g.drawString("C: X- " + xC + " Y- " + yC, 0, 70);
                g.setColor(Color.RED);
            }

            xA1 = p * xA + q * xB;
            yA1 = p * yA + q * yB;
            xB1 = p * xB + q * xC;
            yB1 = p * yB + q * yC;
            xC1 = p * xC + q * xA;
            yC1 = p * yC + q * yA;

            xA = xA1; xB = xB1; xC = xC1;
            yA = yA1; yB = yB1; yC = yC1;
        }
        if(reset)
            angle = 0;
        reset = false;
    }

    public float rotateX(float x, float y, float xR, float yR, float angle) {
        angle *= (Math.PI / 180.0);
        float c = (float)Math.cos(angle), s = (float)Math.sin(angle),
                xF = x - xR, yF = y - yR,
                rx = xF * c - yF * s;

        return rx + xR;
    }

    public float rotateY(float x, float y, float xR, float yR, float angle) {
        angle *= (Math.PI / 180.0);
        float c = (float)Math.cos(angle), s = (float)Math.sin(angle),
                xF = x - xR, yF = y - yR,
                ry = xF * s + yF * c;

        return ry + yR;
    }
}

我一直收到这个

Answer 1

public void paint(Graphics g) {
    super.paintComponent(g);

不知道这是否是唯一的问题，但是自定义绘画是通过重写 paintComponent() 方法完成的：

public void paintComponent(Graphics g) {
    super.paintComponent(g);

编辑：

其他评论，与问题没有直接关系，但对正确设计很重要：

add("South", buttonPanel);
add("Center", drawingPanel);

不要使用硬编码文字。布局管理器将提供您可以使用的变量。另外，不推荐这种形式的 add(...) 方法（阅读 API）。新表格是：

add(buttonPanel, BordeLayout.PAGE_END);
add("Center", BorderLayout.CENTER);

不要使用静态方法和变量。如果您想更改 class 的属性，请创建 "setter" 方法。例如创建一个 setter 方法：

public void setRotate(Boolean rotate)
{
    this.rotate = rotate
    repaint();
}

另外，并不是说 setter 方法调用了 repaint() 方法。这是因为您的自定义 class（不是使用 class 的代码）应该负责重绘。

然后调用setter方法：

//DrawTriangles.rotate = true; // wrong
drawingPanel.setRotate(true);

Answer 2

看起来只有在显示对话框时才会发生这种情况。我已经修改了代码并硬编码了一些值，它没有问题。

if(!reset) {
        if(rotate) {
            angle += Float.parseFloat("15");
            float xR = fx(3),
                    yR = fx(3);
            // other stuff...
        }

我建议你尝试显示对话框并设置相应的值然后重新绘制组件，类似于此：

       shift.addActionListener(new ActionListener() {

       public void actionPerformed(ActionEvent e) {
           float xShift = -DrawTriangles.fx(Integer.parseInt(JOptionPane.showInputDialog("Input X Coordinate for Shift"))),
                   yShift = -DrawTriangles.fx(Integer.parseInt(JOptionPane.showInputDialog("Input Y Coordinate for Shift")));
           drawingPanel.xShift = xShift;
           drawingPanel.yShift = yShift;
           DrawTriangles.shift = true;
           drawingPanel.repaint();
       }
   });

Answer 3

使用BufferedImage修正了绘图，但仍然出现异常。

public void paint(Graphics gg) {
    BufferedImage bf = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);

    Graphics2D g = bf.createGraphics();

    g.setColor(Color.WHITE);
    g.fillRect(0, 0, getWidth(), getHeight());

...

    gg.drawImage(bf, 0, 0, null);

    if(reset)
        angle = 0;
    reset = false;
}

Answer 4

您正在触发 JOptionPane 弹出窗口 在您的 paint() 方法中。

对 .paint() 及其兄弟项的调用应仅限于重绘对象，除此之外别无其他。照原样，您的代码将导致 .paint() 方法阻塞，直到弹出窗口关闭，然后继续处理它停止的地方，可能会拾取仍在屏幕上的工件。正如你在这里看到的，背景被绘制（通过调用 super.paintComponent()）然后弹出窗口被绘制并关闭，然后你的 .paint() 方法的其余部分运行，但是由于背景已经被绘制, 没有重绘弹出窗口所在的位置。

你应该像这样移动代码：

angle += Float.parseFloat(JOptionPane.showInputDialog("Input Angle of Rotation (in degrees)"));
float xR = fx(Integer.parseInt(JOptionPane.showInputDialog("Input X Coordinate for Rotation"))),
      yR = fx(Integer.parseInt(JOptionPane.showInputDialog("Input Y Coordinate for Rotation")));

和

float xShift = -fx(Integer.parseInt(JOptionPane.showInputDialog("Input X Coordinate for Shift"))),
      yShift = -fx(Integer.parseInt(JOptionPane.showInputDialog("Input Y Coordinate for Shift")));

进入适当的 ActionListener 方法，设置必要的值，然后在 paint() 方法中使用它们。

你也应该在使用 .paint() 和 .paintComponent() 时保持一致，就像@camickr 建议的那样，不要有一个方法调用其兄弟的 super。

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