弹出菜单显示后，JButtons消失

Question

我为JButtons添加了弹出菜单的监听器，但是当弹出菜单出现时，JButtons消失了，我需要将光标悬停在按钮上以使它们再次出现。为什么会这样？

（这里的所有方法都在同一个类中）

public Inventory() {
    setLayout(null);
    setBounds(0, 0, 175, 210);

    initPopupMenu(); // this just sets what is inside the popup menu
    int x;
            // 30 buttons
    for(x = 0; x < 30; x++) {
        button[x] = new JButton();
        add(button[x]);
        button[x].addMouseListener(this);
    }

    x = 0;
            // it's a grid of buttons
    for(int i = 0; i < 5; i++) 
        for(int j = 0; j < 6; j++) {
            button[x].setBounds(i*35+1,j*35+1, 33,33);  
            x++;
        }


}

public void mouseClicked(MouseEvent e) {
    for(int j = 0; j < 30; j++) // i tried this one but it still disappears
        button[j].repaint();

    for(int i = 0; i < 30; i++) {
        if(e.getSource() == button[i]) {
            System.out.println("You pressed Button "+i);
            popup.show(e.getComponent(), e.getX(), e.getY());
        }

    }

}

发生了这种情况，

Answer 1

停止使用null布局，似乎这可能是与此相关的问题之一。您的JFrame对我来说似乎有点BLACK，这是您正在使用的THEME或新LOOK AND FEEL，这也可能是导致这种情况发生的原因。在这里检查一下，这里的代码完美无缺：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ButtonPopUp
{
    private static final int SIZE = 30;
    private JButton[] button = new JButton[SIZE];
    private JPopupMenu popup = new JPopupMenu("Hello World");

    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Button POP UP Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setLocationByPlatform(true);

        final JPanel contentPane = new JPanel();
        contentPane.setLayout(new GridLayout(0, 5));

        JMenuItem menuItem1 = new JMenuItem("Menu Item 1");
        JMenuItem menuItem2 = new JMenuItem("Menu Item 2");
        //popup.add(greetings);
        popup.insert(menuItem1, 0);
        popup.insert(menuItem2, 1);

        for (int i = 0; i < SIZE; i++)
        {
            button[i] = new JButton();
            button[i].setBorder(BorderFactory.createEtchedBorder());
            button[i].addMouseListener(new MouseAdapter()
            {
                public void mouseClicked(MouseEvent me)
                {
                    System.out.println("I am WORKING!!");
                    popup.show((JComponent)me.getSource(), me.getX(), me.getY());
                }
            });
            contentPane.add(button[i]);
        }

        frame.getContentPane().add(contentPane);
        frame.setSize(175, 250);
        frame.setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new ButtonPopUp().createAndDisplayGUI();
            }
        });
    }
}

这是输出：