Question

我已经创建了JLabel的自定义子类。我在单个JPanel内的单个JFrame内有一个这样的实例。我不覆盖paintComponent()方法;当光标悬停在它上面时，所有类都会改变背景颜色。

JFrame会立即加载，但几秒钟后JPanel仍然未提取。我通过覆盖paintComponent()并添加一些调试println()语句来验证这是因为我的自定义类。

public void paintComponent(Graphics context)
{
    System.out.println("Painting...");
    super.paintComponent(context);
    System.out.println("Painted.");
}

奇怪的是，当我使用Panel代替JPanel或Label代替JLabel时，会立即绘制它。

这种滞后来自哪里？

编辑：一些示例代码。什么都没画;看一下控制台消息延迟。

import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import java.awt.GridLayout;
import javax.swing.JPanel;

public class Example extends JLabel implements MouseListener
{
    private static final long serialVersionUID = 0;

    public Example()
    {
        super();
        System.out.println("Constructed.");
    }

    public void paintComponent(java.awt.Graphics g)
    {
        System.out.println("Painting component...");
        super.paintComponent(g);
        System.out.println("Painted.");
    }

    public void mouseEntered(MouseEvent event) { }
    public void mouseExited(MouseEvent event) { }
    public void mouseReleased(MouseEvent event) { }
    public void mousePressed(MouseEvent event) { }
    public void mouseClicked(MouseEvent event) { }

    public static void main(final String[] arguments)
    {
        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(1, 1));
        panel.add(new Example());

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(panel);
        frame.setVisible(true);
        System.out.println("Set visible.");
    }
}

Answer 1

我的代码没有滞后：

我的SSCCE：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class LabelTest extends JPanel {
   public LabelTest() {
      add(new MyLabel("Fubar!"));
   }

   private static void createAndShowGui() {
      LabelTest mainPanel = new LabelTest();

      JFrame frame = new JFrame("LabelTest");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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

@SuppressWarnings("serial")
class MyLabel extends JLabel {
   private static final Color BACKGROUND_DEFAULT = new Color(200, 200, 255);
   private static final Color BACKGROUND_MOUSEOVER = new Color(255, 200, 200);
   private static final int PREF_W = 200;
   private static final int PREF_H = 100;

   public MyLabel(String text) {
      super(text, SwingConstants.CENTER);
      setOpaque(true);
      setBackground(BACKGROUND_DEFAULT);
      addMouseListener(new MouseAdapter() {

         @Override
         public void mouseEntered(MouseEvent arg0) {
            setBackground(BACKGROUND_MOUSEOVER);
         }

         @Override
         public void mouseExited(MouseEvent e) {
            setBackground(BACKGROUND_DEFAULT);
         }

      });
   }

   @Override
   public Dimension getPreferredSize() {
      int width = Math.max(super.getPreferredSize().width, PREF_W);
      int height = Math.max(super.getPreferredSize().height, PREF_H);
      return new Dimension(width, height);
   }
}

这告诉我，问题不在于JLabel的概念，其背景通过MouseListener进行更改，而是在代码中的某个地方出现了错误。哪里？谁知道，直到你发布可编辑的可运行代码SSCCE，就像我上面发布的代码一样。

为什么我的自定义Swing标签需要很长时间来初始化？

1 个答案: