在JFrame上绘制线条出现问题

Question

在JFrame上绘制线条出现问题

4

我正在尝试编写一个程序，在屏幕上显示一堆线条，其坐标将从另一个程序确定。

为此，我正在尝试修改jasssuncao在这里的代码，以便我不必点击任何按钮就可以得到线条：如何在Java中绘制线条以下是我现在拥有的：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.LinkedList;

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

public class LineDrawing extends JComponent{

  private static class Line{
      final int x1; 
      final int y1;
      final int x2;
      final int y2;   
      final Color color;

      public Line(int x1, int y1, int x2, int y2, Color color) {
          this.x1 = x1;
          this.y1 = y1;
          this.x2 = x2;
          this.y2 = y2;
          this.color = color;
      }               
  }

  private final LinkedList<Line> lines = new LinkedList<Line>();

  public void addLine(int x1, int x2, int x3, int x4) {
      addLine(x1, x2, x3, x4, Color.black);
  }

  public void addLine(int x1, int x2, int x3, int x4, Color color) {
      lines.add(new Line(x1,x2,x3,x4, color));        
      repaint();
  }

  public void clearLines() {
      lines.clear();
      repaint();
  }

  @Override
  protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      for (Line line : lines) {
          g.setColor(line.color);
          g.drawLine(line.x1, line.y1, line.x2, line.y2);
      }
  }

  public static void main(String[] args) {
      JFrame testFrame = new JFrame();
      testFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      final LineDrawing comp = new LineDrawing();
      comp.setPreferredSize(new Dimension(1000, 400));
      testFrame.getContentPane().add(comp, BorderLayout.CENTER);
      comp.addLine(100, 100, 100, 100, new Color(24, 24, 24));
    testFrame.pack();
    testFrame.setVisible(true);
  }
  }
}

然而，这样做并没有显示任何一行。为什么代码没有显示任何内容？谢谢！

- Valerie Z

1个回答

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- trashgod · Accepted Answer

感谢提供完整的示例，但是有几点需要说明：

Your line needs a non-zero size; note the coordinates required by drawLine():
```
comp.addLine(10, 10, 100, 100, Color.blue);
```
Your JComponent may need to be opaque:
```
comp.setOpaque(true);
```
Construct and manipulate Swing GUI objects only on the event dispatch thread, for example.
Don't use setPreferredSize() when you really mean to override getPreferredSize().