组件分层 Java Swing，悬停时显示层

Question

我有两个JPanels 在同一个容器中相互叠加。我正在使用container.add(jpanel, 0); 和container.add(otherjpanel, 1)。它工作正常，但是为了让顶层显示我必须用鼠标将鼠标悬停在组件上。

这是一些显示我的问题的可执行代码。

只需将鼠标悬停在屏幕上方即可。

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.event.*;
import javax.swing.*;
import javax.swing.text.*;
import java.io.*;
import java.util.*;

public class test {

    public static void main(String args[]) {
        try {
            UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
        } catch (Exception e) {
        }
        JFrame frame = new GUIframe();
        frame.setVisible(true);
        frame.setResizable(false);
    }
}

class GUIframe extends JFrame{

    public GUIframe(){
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setPreferredSize(new Dimension(300,400));
        setSize(300, 400);

        JLayeredPane content = new JLayeredPane();
        content.setPreferredSize(new Dimension(300,400));
        content.setSize(300,400);

        JPanel board = new JPanel();
        for (int i = 0;i<5;i++){
            JButton button = new JButton("button");
            board.add(button);
        }
        content.add(new ImagePanel());
        this.add(content);
        this.add(board);
    }
}

class ImagePanel extends JPanel {
    private Image img;
    String imageLocation = "image location here";

    ImagePanel() {
        img = new ImageIcon(imageLocation).getImage();
        setPreferredSize(new Dimension(300,400));
        setSize(300,400);
        setLayout(null);
        setOpaque(false);
    }

    public void paint(Graphics g){
        super.paint(g);
        g.drawImage(img, 0, 0, this);
    }
}

Answer 1

默认情况下，contentPane 的布局是 BorderLayout。你改变了这个吗？也许您应该将 contentPane 设置为 JLayeredPane。

如果对此建议有任何不清楚的地方，请发表评论。

编辑 1：JLayeredPane 示例
您可以使用我描述的分层窗格来解决此类问题，如下所示，但您必须注意设置大小并使覆盖的 JPanel 不透明：

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.*;

public class Test2 {
   private static final int LP_WIDTH = 450;
   private static final int LP_HEIGHT = 600;
   private static final String IMAGE_SITE = "http://upload.wikimedia.org/wikipedia/"
         + "commons/thumb/b/b8/Laser_Towards_Milky_Ways_Centre.jpg/"
         + "660px-Laser_Towards_Milky_Ways_Centre.jpg";
   private JLayeredPane layeredPanel = new JLayeredPane();

   public Test2() {
      layeredPanel.setPreferredSize(new Dimension(LP_WIDTH, LP_HEIGHT));
      try {
         URL url = new URL(IMAGE_SITE);
         BufferedImage image = ImageIO.read(url);
         ImagePanel2 imagePanel2 = new ImagePanel2(image);
         imagePanel2.setSize(layeredPanel.getPreferredSize());

         JPanel buttonPanel = new JPanel();
         buttonPanel.setOpaque(false);
         for (int i = 0; i < 8; i++) {
            buttonPanel.add(new JButton("Button"));
         }
         buttonPanel.setSize(layeredPanel.getPreferredSize());

         layeredPanel.add(imagePanel2, JLayeredPane.DEFAULT_LAYER);
         layeredPanel.add(buttonPanel, JLayeredPane.PALETTE_LAYER);
      } catch (MalformedURLException e) {
         e.printStackTrace();
         System.exit(-1);
      } catch (IOException e) {
         e.printStackTrace();
         System.exit(-1);
      }
   }

   private JComponent getMainComponent() {
      return layeredPanel;
   }

   private static void createAndShowGui() {
      Test2 test2 = new Test2();

      JFrame frame = new JFrame("Test2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(test2.getMainComponent());
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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

class ImagePanel2 extends JPanel {
   private Image image;

   public ImagePanel2(Image image) {
      this.image = image;
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      if (image != null) {
         g.drawImage(image, 0, 0, null);
      }
   }

}

但是，如果您想要的只是背景图片，那么我会这样做，创建一个使用背景图片的 JPanel，然后向其中添加内容。

import java.awt.*;
import java.awt.image.*;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.*;

public class Test3 extends JPanel {
   private static final int LP_WIDTH = 450;
   private static final int LP_HEIGHT = 600;
   private static final String IMAGE_SITE = "http://upload.wikimedia.org/wikipedia/"
         + "commons/thumb/b/b8/Laser_Towards_Milky_Ways_Centre.jpg/"
         + "660px-Laser_Towards_Milky_Ways_Centre.jpg";

   private BufferedImage image;

   public Test3() {
      try {
         URL url = new URL(IMAGE_SITE);
         image = ImageIO.read(url);

         for (int i = 0; i < 8; i++) {
            add(new JButton("Button"));
         }
      } catch (MalformedURLException e) {
         e.printStackTrace();
         System.exit(-1);
      } catch (IOException e) {
         e.printStackTrace();
         System.exit(-1);
      }
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(LP_WIDTH, LP_HEIGHT);
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      if (image != null) {
         g.drawImage(image, 0, 0, null);
      }
   }

   private static void createAndShowGui() {
      Test3 mainPanel = new Test3();

      JFrame frame = new JFrame("Test3");
      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();
         }
      });
   }
}