java - PropertyChangeListener 中的 JOptionPane.showMessageDialog 导致意外行为

Question

我已经使用 JCheckBoxMenuItem 创建了一个可检查的菜单项。我试图做的是当复选框被选中时，应该会出现一条消息:

 JCheckBoxMenuItem checkbox = new JCheckBoxMenuItem("Checkbox");
    checkbox.addPropertyChangeListener(evt -> {
        boolean isCheck = ((JCheckBoxMenuItem) evt.getSource()).isSelected();
        if(isCheck){
            JOptionPane.showMessageDialog(null, "You checked the checkbox", "Information", JOptionPane.INFORMATION_MESSAGE);
        }
    });

但是，当我尝试选中该复选框时，什么也没有出现。我第二次点击 JMenu 时会出现一堆模态，并导致 ArrayIndexOutOfBoundsException:

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 1 >= 0
at java.util.Vector.elementAt(Vector.java:474)
at javax.swing.MenuSelectionManager.setSelectedPath(MenuSelectionManager.java:117)
at javax.swing.MenuSelectionManager.clearSelectedPath(MenuSelectionManager.java:151)
at javax.swing.plaf.basic.BasicPopupMenuUI$MouseGrabber.cancelPopupMenu(BasicPopupMenuUI.java:917)
at javax.swing.plaf.basic.BasicPopupMenuUI$MouseGrabber.eventDispatched(BasicPopupMenuUI.java:828)
at java.awt.Toolkit$SelectiveAWTEventListener.eventDispatched(Toolkit.java:2425)
at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2317)
at java.awt.Toolkit.notifyAWTEventListeners(Toolkit.java:2275)
at java.awt.Component.dispatchEventImpl(Component.java:4777)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4703)
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$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.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$1.doIntersectionPrivilege(ProtectionDomain.java:75)
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.pumpEventsForFilter(EventDispatchThread.java:109)  
...

是什么导致了这种情况？

Answer 1

What is causing that to happen?

您为错误的工作使用了错误的监听器。 PropertyChangeListener 不是您要实现的目标的合适监听器，相反，您应该使用 ActionListener...

JCheckBoxMenuItem checkbox = new JCheckBoxMenuItem("Checkbox");
checkbox.addActionListener((ActionEvent e) -> {
        boolean isCheck = ((JCheckBoxMenuItem)e.getSource()).isSelected();
        if (isCheck) {
            JOptionPane.showMessageDialog(null, "You checked the checkbox", "Information", JOptionPane.INFORMATION_MESSAGE);
        }
});

PropertyChangeListener 实际上(至少在我的测试下)在 JCheckBoxMenuItem 的选定状态发生更改时不会触发任何事件，但您的代码确实导致它不断抛出弹出一个对话框，迫使我终止程序

看看How to Use Menus , How to Use Buttons, Check Boxes, and Radio Buttons和 How to Write an Action Listeners了解更多详情