Java 在按按钮时渲染矩形时遇到问题

我试图通过按下按钮在面板中添加一个

矩形

，然后用另一个矩形将其删除。它应该可以工作，但它不会呈现任何东西，我绝对不知道为什么

有人能解释一下我做错了什么，并给我一些好的提示，我可以用我的代码改进什么吗

public class GUI extends JPanel {

    public static boolean isRecVisible = false;

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

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        super.paintComponent(g);
        g2d.drawRect(10, 10, 200, 200);
    }

    public static void createGui() {

        int frameWidth = 550;
        int frameHeight = 400;

        int buttonWidth1 = 250;
        int buttonHeight1 = 30;

        int buttonWidth2 = 500;
        int buttonHeight2 = 30;

        int displayWidth = frameWidth - 20;
        int displayHeight = frameHeight - 105;

        GUI drawRec = new GUI();

        JFrame f = new JFrame("Rectangle");
        JPanel p = new JPanel();
        JPanel display = new JPanel();
        JButton addRec = new JButton("Add Rectangle");
        JButton removeRec = new JButton("Remove Rectangle");
        JButton colorRec = new JButton("Color Rectangle");

        f.add(p);
        p.add(addRec);
        p.add(removeRec);
        p.add(colorRec);
        p.add(display);

        display.setBackground(Color.LIGHT_GRAY);

        f.setSize(frameWidth, frameHeight);
        f.setLocationRelativeTo(null);
        f.setResizable(false);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);

        display.setBounds(frameWidth / 2 - displayWidth / 2, 10, displayWidth, displayHeight);
        addRec.setBounds(frameWidth / 2 - buttonWidth1 / 2 - 250 / 2, frameHeight - 85, buttonWidth1, buttonHeight1);
        removeRec.setBounds(frameWidth / 2 - buttonWidth1 / 2 + 250 / 2, frameHeight - 85, buttonWidth1, buttonHeight1);
        colorRec.setBounds(frameWidth / 2 - buttonWidth2 / 2, frameHeight - 60, buttonWidth2, buttonHeight2);

        addRec.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (isRecVisible == false) {
                    isRecVisible = true;
                    display.add(drawRec);
                    display.repaint();
                    System.out.println("Rectangle has been drawn!");

                } else {
                    System.out.println("Rectangle has already been drawn!");
                    return;
                }
            }
        });

        removeRec.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (isRecVisible == true) {
                    isRecVisible = false;
                    System.out.println("Rectangle has been removed!");

                } else {
                    System.out.println("Rectangle has already been removed");
                    return;
                }
            }
        });
    }
}

将组件添加（或删除）到可见框架时，基本逻辑是：

display.add(...);
display.revalidate();
display.repaint(); // sometimes needed

revalidate（）

是关键方法，因为它调用布局管理器，以便可以设置组件的大小/位置

但是，这仍然无法解决问题，因为您的自定义面板没有首选的大小，因此您的组件没有可绘制的内容

您需要覆盖自定义面板的

getPreferredSize（）

方法，以返回自定义组件的首选大小。因此，在您的情况下，您可以将首选大小设置为（220220），以便矩形在面板中居中

有关更多信息和完整的工作示例，请阅读上的Swing教程部分

---

注意：教程示例还将向您展示如何更好地构造代码，以确保在事件调度线程上创建GUI

与其添加或删除组件，不如在构造时添加自定义绘制的面板，并使用

isRecVisible

布尔值作为标记来测试绘制矩形

如图所示：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class GUI extends JPanel {

    public static boolean isRecVisible = false;

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

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        super.paintComponent(g);
        if (isRecVisible) {
            g2d.drawRect(10, 10, 200, 200);
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(600,400);
    }

    public static void createGui() {
        int frameWidth = 550;
        int frameHeight = 400;

        GUI drawRec = new GUI();
        drawRec.setBackground(Color.LIGHT_GRAY);

        JFrame f = new JFrame("Rectangle");
        JPanel p = new JPanel();
        JButton addRec = new JButton("Add Rectangle");
        JButton removeRec = new JButton("Remove Rectangle");
        JButton colorRec = new JButton("Color Rectangle");

        f.add(p, BorderLayout.PAGE_START);
        p.add(addRec);
        p.add(removeRec);
        p.add(colorRec);
        f.add(drawRec);

        f.setSize(frameWidth, frameHeight);
        f.setLocationRelativeTo(null);
        f.setResizable(false);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);

        addRec.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isRecVisible = true;
                drawRec.repaint();
            }
        });

        removeRec.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isRecVisible = false;
                drawRec.repaint();
            }
        });
    }
}

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class GUI extends JPanel {

    public static boolean isRecVisible = false;

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

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        super.paintComponent(g);
        if (isRecVisible) {
            g2d.drawRect(10, 10, 200, 200);
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(600,400);
    }

    public static void createGui() {
        int frameWidth = 550;
        int frameHeight = 400;

        GUI drawRec = new GUI();
        drawRec.setBackground(Color.LIGHT_GRAY);

        JFrame f = new JFrame("Rectangle");
        JPanel p = new JPanel();
        JButton addRec = new JButton("Add Rectangle");
        JButton removeRec = new JButton("Remove Rectangle");
        JButton colorRec = new JButton("Color Rectangle");

        f.add(p, BorderLayout.PAGE_START);
        p.add(addRec);
        p.add(removeRec);
        p.add(colorRec);
        f.add(drawRec);

        f.setSize(frameWidth, frameHeight);
        f.setLocationRelativeTo(null);
        f.setResizable(false);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);

        addRec.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isRecVisible = true;
                drawRec.repaint();
            }
        });

        removeRec.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isRecVisible = false;
                drawRec.repaint();
            }
        });
    }
}