Java JPopupMenu 错误

Java JPopupMenu bug(Java JPopupMenu 错误)

问题描述

好像我在 Java 中发现了一个错误:

Seems like I've found a bug in Java:

我需要创建具有透明背景的 JFrame，现在我需要为某些用户操作显示 JPopupMenu.当 JPopupMenu 完全位于 JFrame 内时，它可以正常工作.但是当 JPopupMenu 部分在 JFrame 之外时，没有项目可见.

I need to create the JFrame with a transparent background and now I need to show the JPopupMenu for some user actions. It works fine when JPopupMenu is housed fully inside a JFrame. But when the JPopupMenu is partly outside the JFrame, no item is visible.

SSCCE:

public class PopupTest {
    public static void main(String[] a) {
        final JFrame frame = new JFrame();
        frame.setSize(500, 500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JPanel panel = new JPanel(new BorderLayout());
        panel.setBorder(BorderFactory.createLineBorder(Color.RED));

        panel.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if (e.getButton() == MouseEvent.BUTTON3) {
                    JPopupMenu menu = new JPopupMenu();
                    for (int i = 0 ; i < 10; i++) {
                        menu.add(String.valueOf(i));
                    }

                    menu.show(panel, e.getX(), e.getY());
                }
            }
        });
        frame.setContentPane(panel);
        frame.setUndecorated(true);
        frame.setBackground(new Color(50, 50, 50, 200));

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                frame.setVisible(true);
            }
        });
    }
}

有人知道怎么解决吗?

PS: JDK 7u40，Win x64

PS: JDK 7u40, Win x64

推荐答案

这是Oracle JDK 7中的bug(顺便说一下在Open JDK 7中无法重现).

This is bug in Oracle JDK 7 (it cannot be reproduced in Open JDK 7 by the way).

要解决此问题，您可以制定一种解决方法(是的，这只是一种解决方法，不能保证它不会因某些 Java 更新而中断)，以便为弹出菜单创建的窗口将变得不透明，因为它一出现，就会正确显示.最起码到现在.以下是 Java 7 及更高版本的实现方式:

To fix this you can make a workaround (yes, this is just a workaround, there is no guarantees that it won't break with some Java update) so that the window created for popup-menu will become non-opaque as soon as it shows up, then it will be displayed properly. Atleast for now. Here is how this can be done for Java version 7 and later:

PropertyChangeListener propertyChangeListener = new PropertyChangeListener ()
{
    @Override
    public void propertyChange ( final PropertyChangeEvent evt )
    {
        if ( evt.getNewValue () == Boolean.TRUE )
        {
            // Retrieving popup menu window (we won't find it if it is inside of parent frame)
            final Window ancestor = getWindowAncestor ( popupMenu );
            if ( ancestor != null && ancestor.getClass ().getCanonicalName ().endsWith ( "HeavyWeightWindow" ) )
            {
                // Checking that parent window for our window is opaque, only then setting opacity
                final Component parent = ancestor.getParent ();
                if ( parent != null && parent instanceof Window && parent.getBackground ().getAlpha () == 0 )
                {
                    // Making popup menu window non-opaque
                    ancestor.setBackground ( new Color ( 0, 0, 0, 0 ) );
                }
            }
        }
    }

    private Window getWindowAncestor ( Component component )
    {
        if ( component == null )
        {
            return null;
        }
        if ( component instanceof Window )
        {
            return ( Window ) component;
        }
        for ( Container p = component.getParent (); p != null; p = p.getParent () )
        {
            if ( p instanceof Window )
            {
                return ( Window ) p;
            }
        }
        return null;
    }
};
popupMenu.addPropertyChangeListener ( "visible", propertyChangeListener );

如果您还想支持 JDK 6 版本，则必须付出更多努力，因为该代码甚至无法在早期 JDK 版本上编译(在早期版本的 Window 中没有set/getBackground"方法).

You will have to put some more effort if you also want to support JDK 6- versions because that code won't even compile on earlier JDK versions (there are no "set/getBackground" methods in Window in earlier versions).

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