JTextArea 显示行号

淡淡的烟草味﹌ 2024-04-07 14:43 77阅读 0赞

#### JTextArea 显示行号 ####

*  1.需求描述
 *  2.代码实现
 *  3.效果演示

> 系统：Win10  
> JDK：1.8.0\_333  
> IDEA：2020.3.4

## 1.需求描述 ##

最近在做一个 Swing 项目的时候，使用到了 JTextArea 组件，然后需要显示文本处于多少行，在左边需要显示它的行号，并且会随着行号的增加，显示行号的面板的宽度会自动扩展开

## 2.代码实现 ##

import javax.swing.*;
    import javax.swing.text.BadLocationException;
    import javax.swing.text.Document;
    import java.awt.*;
    
    /**
     * @ClassName MyTextArea
     * @Description 实现 JTextArea 显示行号
     * @Author Li
     * @Date 2022/8/28 13:55
     * @ModifyDate 2022/8/28 13:55
     * @Version 1.0
     */
    public class MyTextArea extends JPanel {
        
        private LinePanel linePanel;
    
        private JTextArea textArea;
    
        private JScrollPane scrollPane;
    
        public MyTextArea() {
        
            this.setLayout(new BorderLayout());
            linePanel = new LinePanel();
            linePanel.setPreferredSize(new Dimension(25, 10));
            this.textArea = new JTextArea() {
        
                public void paint(Graphics g) {
        
                    super.paint(g);
                    linePanel.repaint();
                }
            };
            this.scrollPane = new JScrollPane(this.textArea);
            this.add(linePanel, BorderLayout.WEST);
            this.add(scrollPane, BorderLayout.CENTER);
        }
    
        // 内部类：显示行号的面板
        private class LinePanel extends JPanel {
        
            @Override
            public void paint(Graphics g) {
        
                super.paint(g);
                // starting pos in document
                int start = textArea.viewToModel(scrollPane.getViewport().getViewPosition());
                // end pos in doc
                int end = textArea.viewToModel(new Point(scrollPane.getViewport().getViewPosition().x + textArea.getWidth()
                        , scrollPane.getViewport().getViewPosition().y + textArea.getHeight()));
    
                // translate offsets to lines
                Document doc = textArea.getDocument();
                int startLine = doc.getDefaultRootElement().getElementIndex(start) + 1;
                int endLine = doc.getDefaultRootElement().getElementIndex(end) + 1;
    
                int fontHeight = g.getFontMetrics(textArea.getFont()).getHeight();
                int fontDesc = g.getFontMetrics(textArea.getFont()).getDescent();
                int starting_y = -1;
                
                try {
        
                    starting_y = textArea.modelToView(start).y -
                            scrollPane.getViewport().getViewPosition().y + fontHeight - fontDesc;
                } catch (BadLocationException ble) {
        
                    ble.printStackTrace();
                }
    
                for (int line = startLine, y = starting_y; line <= endLine; y += fontHeight, line++) {
        
                    g.drawString(Integer.toString(line), getNumX(line), y);
                }
            }
    
            // 获取当前行的行号 x 坐标
            private int getNumX(int line) {
        
                int width = linePanel.getWidth() - 5;
                FontMetrics metrics = linePanel.getFontMetrics(this.getFont());
                int fontHeight = metrics.getHeight();
                int fontWidth = metrics.stringWidth("0");
                int digit = 0;
                while (line > 0) {
        
                    line = line / 10;
                    digit++;
                }
                int x = width - digit * fontWidth;
                // 自适应调整宽度
                if (x < 5) {
        
                    linePanel.setPreferredSize(new Dimension(getWidth() + fontWidth, fontHeight));
                    linePanel.updateUI();
                }
                return x;
            }
        }
    
        // 主方法测试
        public static void main(String[] args) {
        
            JFrame frame = new JFrame();
            frame.setTitle("JTextArea显示行号");
            frame.setLayout(new BorderLayout());
            MyTextArea textArea = new MyTextArea();
            frame.getContentPane().add(textArea, BorderLayout.CENTER);
            frame.setSize(new Dimension(400, 300));
            frame.setLocationRelativeTo(null);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
        }
    }

## 3.效果演示 ##

![在这里插入图片描述][1a0e276789c644c19fe8362cda973c86.gif]

[1a0e276789c644c19fe8362cda973c86.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/07/f42be097514245138b891eefd3739946.gif