在面板内绘制图像

Question

我有一个带有两个按钮的面板。我正在尝试在面板内插入图像，我想在单击按钮后在图像内画线。我使用了下面的代码，但这似乎不起作用。

public class Try_Panel extends JFrame {
  // start attributes
  private JPanel jPanel1 = new JPanel(null, true);
  private JButton jButton1 = new JButton();
  private JButton jButton2 = new JButton();
  // end attributes

  public Try_Panel(String title) {
    // Frame-Init
    super(title);
    setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
    int frameWidth = 300; 
    int frameHeight = 300;
    setSize(frameWidth, frameHeight);
    Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
    int x = (d.width - getSize().width) / 2;
    int y = (d.height - getSize().height) / 2;
    setLocation(x, y);
    setResizable(false);
    Container cp = getContentPane();
    cp.setLayout(null);
    // start components

    jPanel1.setBounds(48, 24, 209, 145);
    jPanel1.setOpaque(false);
    cp.add(jPanel1);
    jButton1.setBounds(88, 208, 75, 25);
    jButton1.setText("jButton1");
    jButton1.setMargin(new Insets(2, 2, 2, 2));
    jButton1.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt) { 
        jButton1_ActionPerformed(evt);
      }
    });
    cp.add(jButton1);
    jButton2.setBounds(184, 208, 75, 25);
    jButton2.setText("jButton2");
    jButton2.setMargin(new Insets(2, 2, 2, 2));
    jButton2.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt) { 
        jButton2_ActionPerformed(evt);
      }
    });
    cp.add(jButton2);
    // end components

    setVisible(true);
  } // end of public Try_Panel

  // start methods
  public void jButton1_ActionPerformed(ActionEvent evt) {
      BufferedImage image=new BufferedImage(jPanel1.getWidth(), jPanel1.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
        JLabel l=new JLabel(new ImageIcon(image));
        Graphics graphics = image.getGraphics();
        Graphics2D g = (Graphics2D) graphics;
        g.fillRect(0, 0, image.getWidth(), image.getHeight());
        g.setColor(Color.BLUE);
        g.drawLine(0, 0, 300, 400);
        jPanel1.add(l);
  } // end of jButton1_ActionPerformed

  public void jButton2_ActionPerformed(ActionEvent evt) {
    // TODO add your code here
  } // end of jButton2_ActionPerformed

  // end methods

  public static void main(String[] args) {
    new Try_Panel("Try_Panel");
  } // end of main

} // end of class Try_Panel

最大的问题是我的其他班级使用的相同代码。

Answer 1

尝试image在ImageIcon更新后包装内部。同样，Graphics#dispose当您完成对图形上下文的渲染时，还应该调用。

    public void jButton1_ActionPerformed(ActionEvent evt) {
        BufferedImage image=new BufferedImage(jPanel1.getWidth(), jPanel1.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
        Graphics2D g = image.createGraphics();
        g.fillRect(0, 0, image.getWidth(), image.getHeight());
        g.setColor(Color.BLUE);
        g.drawLine(0, 0, 300, 400);
        g.dispose();
        JLabel l=new JLabel(new ImageIcon(image));
        jPanel1.add(l);
    }

您还应该依靠布局管理器，而不是自己动手做，这只会使您的生活更轻松。

就个人而言，我认为将其直接绘制到自定义组件会更容易JPanel。查看执行自定义绘画以获取更多详细信息

用示例更新

基本上，我将您的示例更改为

1. 使用布局管理器
2. 在EDT上下文中加载UI
3. revalidate 的 jPanel1

    public class BadLabel extends JFrame {
        // start attributes

        private JPanel jPanel1 = new JPanel(new BorderLayout(), true);
        private JButton jButton1 = new JButton();
        private JButton jButton2 = new JButton();
        // end attributes

        public BadLabel(String title) {
            // Frame-Init
            super(title);
            setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
            int frameWidth = 300;
            int frameHeight = 300;
            setSize(frameWidth, frameHeight);
            Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
            int x = (d.width - getSize().width) / 2;
            int y = (d.height - getSize().height) / 2;
            setLocation(x, y);
    //        setResizable(false);
            Container cp = getContentPane();
    //        cp.setLayout(null);
            // start components

    //        jPanel1.setBounds(48, 24, 209, 145);
            jPanel1.setOpaque(true);
            jPanel1.setBackground(Color.RED);
            cp.add(jPanel1);

            JPanel buttons = new JPanel();
    //        jButton1.setBounds(88, 208, 75, 25);
            jButton1.setText("jButton1");
            jButton1.setMargin(new Insets(2, 2, 2, 2));
            jButton1.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent evt) {
                    jButton1_ActionPerformed(evt);
                }
            });
            buttons.add(jButton1);
    //        jButton2.setBounds(184, 208, 75, 25);
            jButton2.setText("jButton2");
            jButton2.setMargin(new Insets(2, 2, 2, 2));
            jButton2.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent evt) {
                    jButton2_ActionPerformed(evt);
                }
            });
            buttons.add(jButton2);
            // end components

            cp.add(buttons, BorderLayout.SOUTH);

            setVisible(true);
        } // end of public BadLabel

        // start methods
        public void jButton1_ActionPerformed(ActionEvent evt) {
            BufferedImage image = new BufferedImage(jPanel1.getWidth(), jPanel1.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
            Graphics2D g = image.createGraphics();
            g.fillRect(0, 0, image.getWidth(), image.getHeight());
            g.setColor(Color.BLUE);
            g.drawLine(0, 0, 300, 400);
            g.dispose();
            JLabel l = new JLabel(new ImageIcon(image));
            l.setBorder(new LineBorder(Color.BLUE));
            jPanel1.add(l);
            jPanel1.revalidate();
        } // end of jButton1_ActionPerformed

        public void jButton2_ActionPerformed(ActionEvent evt) {
            // TODO add your code here
        } // end of jButton2_ActionPerformed

        // end methods
        public static void main(String[] args) {
            EventQueue.invokeLater(new Runnable() {
                @Override
                public void run() {
                    try {
                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    } catch (Exception exp) {
                    }
                    new BadLabel("BadLabel");
                }
            });
        } // end of main
    } // end of class BadLabel}