java - JButton 的操作调用了 focusLost 事件。这怎么可能？

Question

我们的一位客户报告我们的应用程序出现异常。问题是，我完全无法理解如何重现此错误。

代码如下:

btn.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        popup.show(btn, 3, btn.getHeight());
    }
});

注释:

• btn 是 JButton 类型的最终局部变量。
• popup 是 JPopupMenu 类型的最终局部变量。

抛出以下异常:

java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
    at java.awt.Component.getLocationOnScreen_NoTreeLock(Unknown Source)
    at java.awt.Component.getLocationOnScreen(Unknown Source)
    at javax.swing.JPopupMenu.show(Unknown Source)
    at fr.def.iss.vd2.mod_site_watcher_gui.SiteElementPanel$4.actionPerformed(SiteElementPanel.java:117)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.focusLost(Unknown Source)
    at java.awt.Component.processFocusEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
    at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
    at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$2.run(Unknown Source)
    at java.awt.EventQueue$2.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

据我所知，show 方法提示 btn 没有显示。调用 actionPerformed 方法时 btn 怎么可能不显示？

此堆栈跟踪中最奇怪的是 actionPerformed 方法似乎在处理 FocusEvent 时被触发(实际上是 focusLost ).

问题是:您能解释一下这个堆栈跟踪是如何发生的吗？

结语

感谢trashgod的建议，我找到了问题。

在 Windows 上，当按钮在被按下时消失，然后它的 ActionListeners 被触发，就像按钮被点击一样。这种行为可以在 Windows 上观察到，但不能在 Linux 上观察到。

我在 Oracle/Sun 错误数据库上提交了错误。这是链接:

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7115421

(此链接将在几天内生效，经过 Java 团队审核后)。

感谢您的帮助。 trashgod 和 Thomas 的回答帮了大忙。

Answer 1

一个可能的来源是竞争条件，它允许事件在接收者可见之前触发。验证您的 Swing GUI 对象仅是在 event dispatch thread 上构建和操作的.文章Debugging Swing, the final summary引用于 How to generate exceptions from RepaintManager提到了几种自动搜索的方法。