在 JFrame 中创建 JPanel，并使用 paintComponent() 方法绘制面板答案

【问题标题】：Creating a JPanel in a JFrame, and drawing the panel, using paintComponent() method在 JFrame 中创建 JPanel，并使用 paintComponent() 方法绘制面板
【发布时间】：2015-10-15 08:22:37
【问题描述】：

这是我第一次使用java Swing，我不知道如何在JSplitPane中具体的JPanel进行绘画，我尝试创建一个新类来实现paintComponent方法，但是它不能被覆盖。有人可以帮我吗？

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

public class SplitPane extends JPanel{

    private JPanel mainPanel;
    private JPanel leftPanel;
    private JPanel rightPanel;


    public SplitPane() {

    }

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new SplitPane().createAndShowUI();
            }
        });
    }

    private void createAndShowUI() {
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 500);
        initComponents(frame.getContentPane());
        frame.setVisible(true);
    }

    private void initComponents(Container contentPane) {
        mainPanel = new JPanel();
        leftPanel = new JPanel();
        rightPanel = new JPanel();
        leftPanel.add(new JLabel("left"));
        rightPanel.add(new JLabel("right"));
        leftPanel.setPreferredSize(new Dimension(200, 40));
        rightPanel.setPreferredSize(new Dimension(280, 400));
        leftPanel.setBackground(Color.WHITE);
        rightPanel.setBackground(Color.WHITE);

        JSplitPane mainJsp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
        mainJsp.add(leftPanel, JSplitPane.TOP);
        mainJsp.add(rightPanel, JSplitPane.BOTTOM);
        mainJsp.setOneTouchExpandable(true);
        mainJsp.setDividerLocation(150);
        mainPanel.add(mainJsp);
        contentPane.add(mainPanel);

        leftPanel = new PaintPanel();


    }

    public class PaintPanel extends JPanel {
        public PaintPanel() {
            System.out.println("PaintPanel");
            this.setLayout(new BorderLayout());
            this.setPreferredSize(new Dimension(300, 300));
        }

        @Override
        public void paintComponent(Graphics g) {

            System.out.println("12345678");
            super.paintComponent(g);
            //g.setColor(Color.black);
            g.drawRect(3, 3, 20, 20);
        }
    }
}

【问题讨论】：

public void paintComponents(Graphics g) { 应该是 public void paintComponent(Graphics g) {（否 S）。进一步的public void paintComponent(Graphics g) { .. 应该是public void paintComponent(Graphics g) { super.paintComponent(g); ..
另见Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?（是的。）
谢谢！它仍然不起作用，我在paintComponent函数中使用了system.out.print，但是控制台中没有打印出来，所以我认为这个函数没有被覆盖。
您永远不会将面板添加到任何容器中。没有add(middleRightPanel)等行
如需尽快获得更好的帮助，请发帖 minimal reproducible example 或 Short, Self Contained, Correct Example。请注意，MCVE 应包含 import 语句和 main(String[]) 以运行它。

标签： java swing jpanel java-2d

【解决方案1】：

你永远不会在任何东西上添加PaintPanel，例如...

private void initComponents(Container contentPane) {
    mainPanel = new JPanel();
    leftPanel = new JPanel();
    rightPanel = new JPanel();
    leftPanel.add(new JLabel("left"));
    rightPanel.add(new JLabel("right"));
    leftPanel.setPreferredSize(new Dimension(200, 40));
    rightPanel.setPreferredSize(new Dimension(280, 400));
    leftPanel.setBackground(Color.WHITE);
    rightPanel.setBackground(Color.WHITE);

    JSplitPane mainJsp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
    mainJsp.add(leftPanel, JSplitPane.TOP);
    mainJsp.add(rightPanel, JSplitPane.BOTTOM);
    mainJsp.setOneTouchExpandable(true);
    mainJsp.setDividerLocation(150);
    mainPanel.add(mainJsp);
    contentPane.add(mainPanel);

    leftPanel = new PaintPanel();
    // Just left hanging here, never added to anything...?

}

所以，如果我把它改成...

private void initComponents(Container contentPane) {
    mainPanel = new JPanel();
    leftPanel = new PaintPanel();
    rightPanel = new JPanel();
    leftPanel.add(new JLabel("left"));
    rightPanel.add(new JLabel("right"));
    leftPanel.setPreferredSize(new Dimension(200, 40));
    rightPanel.setPreferredSize(new Dimension(280, 400));
    leftPanel.setBackground(Color.WHITE);
    rightPanel.setBackground(Color.WHITE);

    JSplitPane mainJsp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
    mainJsp.add(leftPanel, JSplitPane.TOP);
    mainJsp.add(rightPanel, JSplitPane.BOTTOM);
    mainJsp.setOneTouchExpandable(true);
    mainJsp.setDividerLocation(150);
    mainPanel.add(mainJsp);
    contentPane.add(mainPanel);

    //leftPanel = new PaintPanel();

}

现在显示...

【讨论】：