Java Swing -改变鼠标监听器的JComponent不透明度

Question

就像标题所说的那样-我有一个JPanel，如果不活动，我想让它的不透明度为90%，如果鼠标悬停，则为完全不透明度。

我已经有了单独的组件工作-鼠标在上面和外面是OK的，我可以改变不透明度从覆盖paintComponent方法，但我想我有问题与MouseAdapter和paintComponent之间的连接。

似乎有一种非常简单的方法可以做到这一点——有什么建议吗?

(顺便说一句，抱歉把代码留在家里了，所以现在没有例子:(除非它不能快速解决，否则我明天会抛出一些代码)

Answer 1

如果您要覆盖paintComponent方法，您应该能够向JPanel扩展添加一个不透明度变量。在MouseAdapter中修改这个(使用mutator)。然后在重写的paintComponent方法中引用该变量来确定如何绘制。

Answer 2

如果你已经覆盖了paintComponent方法，我建议你让MouseAdapter成为Panel的一个匿名内部类，并让它操作一个私有布尔标志。

public class FadingPanel extends JPanel
{
    private boolean active;
    public FadingPanel()
    {
        createMouseAdapter();
    }
    private void createMouseAdapter()
    {
        this.addMouseListener(new MouseAdapter()
        {
            // your mouseadapter code here toggling the active flag
        } 
    }
    @Override
    public boolean paintComponent(Graphics g)
    {
         if(active)
         {
              super.paintComponent(g);
         }
         else
         {
              // your semitransparent painting code here
         }
    }
}

Answer 3

哎呀，我没有Haase和Guy的书，我不记得他们推荐的半透明组件的编码方式，但我猜重写paint或paintComponent工作，除了重写paint将从一开始就显示对子组件的影响。例如:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class OpaqueJPanels {
   private static void createAndShowUI() {
      JPanel mainPanel = new JPanel(new GridLayout(1, 0));
      mainPanel.add(new OpaqueJPanel(false, "Override paintComponent"));
      mainPanel.add(new OpaqueJPanel(true, "Override paint"));
      JFrame frame = new JFrame("Opaque JPanels");
      frame.getContentPane().add(mainPanel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }
   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}
class OpaqueJPanel extends JPanel {
   private static final int OJP_WIDTH = 250;
   private static final int OJP_HEIGHT = OJP_WIDTH;
   private static final Composite TRANSLUSCENT_COMPOSITE = AlphaComposite
            .getInstance(AlphaComposite.SRC_OVER, 0.4f);
   private static final Composite NON_TRANSLUSCENT_COMPOSITE = AlphaComposite
            .getInstance(AlphaComposite.SRC_OVER, 1.0f);
   private boolean overridePaint;
   private boolean transluscent = true;
   public OpaqueJPanel(boolean overridePaint, String title) {
      add(new JButton("Button"));
      setBorder(BorderFactory.createTitledBorder(title));
      addMouseListener(new MouseAdapter() {
         @Override
         public void mouseEntered(MouseEvent e) {
            transluscent = false;
            getParent().repaint();
         }
         @Override
         public void mouseExited(MouseEvent e) {
            if (!OpaqueJPanel.this.contains(e.getPoint())) {
               transluscent = true;
               getParent().repaint();
            }
         }
      });
   }
   @Override
   public Dimension getPreferredSize() {
      return new Dimension(OJP_WIDTH, OJP_HEIGHT);
   }
   @Override
   public void paint(Graphics g) {
      if (!overridePaint) {
         super.paint(g);
         return;
      }
      Graphics2D g2 = (Graphics2D) g;
      Composite composite = transluscent ? TRANSLUSCENT_COMPOSITE
               : NON_TRANSLUSCENT_COMPOSITE;
      g2.setComposite(composite);
      super.paint(g);
   }
   @Override
   protected void paintComponent(Graphics g) {
      if (overridePaint) {
         super.paintComponent(g);
         return;
      }
      Graphics2D g2 = (Graphics2D) g;
      Composite composite = transluscent ? TRANSLUSCENT_COMPOSITE
               : NON_TRANSLUSCENT_COMPOSITE;
      g2.setComposite(composite);
      super.paintComponent(g);
   }
}

我还发现，如果我重新绘制JPanel的父组件而不是JPanel本身，效果会更好。