JInternalFrame动态显示和隐藏标题栏

Question

一开始，我的JInternalFrame的标题栏是隐藏的(((BasicInternalFrameUI) iw.getUI()).setNorthPane(null))。鼠标一进入框架边框，我就想再次显示标题栏，直到边框或标题栏本身触发一个mouseExit。

这是我的第一次试验：

public class InternalWindow extends JInternalFrame{
    public InternalWindow(){
        ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
        setResizable(true);
        setVisible(true);

        addMouseListener(new MouseAdapter() {
            @Override
            public void mouseEntered(MouseEvent e) {
                ((BasicInternalFrameUI) iw.getUI()).setNorthPane(new BasicInternalFrameTitlePane(iw));
                ((BasicInternalFrameUI) iw.getUI()).getNorthPane().revalidate();
                ((BasicInternalFrameUI) iw.getUI()).getNorthPane().repaint();
                setFrameIcon(null);
                revalidate();
                repaint();
                ((BasicInternalFrameUI) iw.getUI()).getNorthPane().addMouseListener(new MouseAdapter() {
                    @Override
                    public void mouseExited(MouseEvent e) {
                        ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
                        revalidate();
                        repaint();
                    }
                });
            }
            @Override
            public void mouseExited(MouseEvent e) {
                ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
                revalidate();
                repaint();
            }
        });
    }
}

但是标题栏不能正确绘制，并且不会对交互做出反应。(picture here)

所以我尝试了另一种方式：

public class InternalWindow extends JInternalFrame{
    public InternalWindow(){
        ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
        setResizable(true);
        setVisible(true);

        addMouseListener(new MouseAdapter() {
            @Override
            public void mouseEntered(MouseEvent e) {
                updateUI();
                setFrameIcon(null);
                ((BasicInternalFrameUI) iw.getUI()).getNorthPane().addMouseListener(new MouseAdapter() {
                    @Override
                    public void mouseExited(MouseEvent e) {
                        ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
                        revalidate();
                        repaint();
                    }
                });
            }
            @Override
            public void mouseExited(MouseEvent e) {
                ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
                revalidate();
                repaint();
            }
        });
    }
}

这样标题栏才能正确绘制，但因此AWT-EventQueue抛出一个异常，阻止调用附加到边框的mouseExited：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.plaf.basic.BasicInternalFrameUI.updateFrameCursor(BasicInternalFrameUI.java:317)
    at javax.swing.plaf.basic.BasicInternalFrameUI$BorderListener.mouseEntered(BasicInternalFrameUI.java:1086)
    at java.awt.AWTEventMulticaster.mouseEntered(AWTEventMulticaster.java:300)
    at java.awt.Component.processMouseEvent(Component.java:6544)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6300)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4891)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4713)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.retargetMouseEnterExit(Container.java:4676)
    at java.awt.LightweightDispatcher.trackMouseEnterExit(Container.java:4654)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4505)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2750)
    at java.awt.Component.dispatchEvent(Component.java:4713)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

不是有一种简单的方法来动态隐藏和显示标题栏吗？

Answer 1

好吧，我只是发现了一些技巧，简单地为边界的mouseEntered和mouseExited注册了两个单独的MouseListeners，并在mouseEntered中删除了mouseExited的那个，并在标题栏的mouseExited中读取了它。但我相信一定有更优雅的方式来实现这一点……

    MouseAdapter ma1 = new MouseAdapter() {
        @Override
        public void mouseExited(MouseEvent e) {
            ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
            revalidate();
            repaint();
        }
    };

    addMouseListener(new MouseAdapter() {
        @Override
        public void mouseEntered(MouseEvent e) {
            updateUI();
            setFrameIcon(null);
            ((BasicInternalFrameUI) iw.getUI()).getNorthPane().addMouseListener(new MouseAdapter() {
                @Override
                public void mouseExited(MouseEvent e) {
                    ((BasicInternalFrameUI) iw.getUI()).setNorthPane(null);
                    revalidate();
                    repaint();
                    addMouseListener(ma1);
                }
            });
            removeMouseListener(ma1);
        }
    });