Java JPopupMenu bug [英] Java JPopupMenu bug

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 JFrame 透明背景，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，没有任何项目可见。

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);
            }
        });
    }
}

有谁知道如何解决这个问题？

Does anyone know how to solve this?

PS： JDK 7u40，Win x64

PS: JDK 7u40, Win x64

推荐答案

这是Oracle JDK 7中的错误（顺便说一下，它无法在Open JDK 7中重现）。

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

要解决这个问题，你可以做一个解决方法（是的，这是只是一个解决方法，不能保证它不会破坏某些Java更新），因此为弹出菜单创建的窗口一旦显示就会变为非不透明，然后它将正确显示。至少现在（是。以下是Java 7及更高版本的完成方式：

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 );

如果你还想支持JDK 6版本，你将不得不付出更多的努力，因为那些代码甚至不会在早期的JDK版本上编译（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).

这篇关于Java JPopupMenu bug的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！