java - 为什么在处理后 JDialog 中 formWindowClosed 被触发两次

Question

Show prompt before closing JFrame

我希望在我们真正退出应用程序之前提示用户输入。到目前为止，以下技术对于 JFrame 效果很好。

public class JavaApplication1 extends javax.swing.JFrame {

    public JavaApplication1() {
        this.setDefaultCloseOperation(javax.swing.WindowConstants.DO_NOTHING_ON_CLOSE);

        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosed(java.awt.event.WindowEvent evt) {
                formWindowClosed(evt);
            }
            public void windowClosing(java.awt.event.WindowEvent evt) {
                formWindowClosing(evt);
            }
        });        
    }

    private void formWindowClosing(java.awt.event.WindowEvent evt) {                                
        System.out.println("formWindowClosing : Are you sure you want to quit?");
        if (true)
            this.dispose();
    }

    private void formWindowClosed(java.awt.event.WindowEvent evt) {
        System.out.println("formWindowClosed");
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JavaApplication1 m = new JavaApplication1();

                m.setSize(300, 200);

                m.setVisible(true);
            }
        });
    }
}

将打印以下内容

formWindowClosing : Are you sure you want to quit?
formWindowClosed

但是，当我从 JFrame 更改为 JDialog 时，formWindowClosed 被调用两次!

formWindowClosing : Are you sure you want to quit?
formWindowClosed
formWindowClosed

这里是代码

public class JavaApplication1 extends javax.swing.JDialog {

    public JavaApplication1() {
        this.setDefaultCloseOperation(javax.swing.WindowConstants.DO_NOTHING_ON_CLOSE);

        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosed(java.awt.event.WindowEvent evt) {
                formWindowClosed(evt);
            }
            public void windowClosing(java.awt.event.WindowEvent evt) {
                formWindowClosing(evt);
            }
        });        
    }

    private void formWindowClosing(java.awt.event.WindowEvent evt) {                                
        System.out.println("formWindowClosing : Are you sure you want to quit?");
        if (true)
            this.dispose();
    }

    private void formWindowClosed(java.awt.event.WindowEvent evt) {
        System.out.println("formWindowClosed");
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JavaApplication1 m = new JavaApplication1();

                m.setSize(300, 200);

                m.setVisible(true);
            }
        });
    }
}

我可以知道为什么会这样吗？这是一个错误吗？我怎样才能防止这种情况发生？我不想使用 System.exit，因为此对话框可能是子对话框，而不是主应用程序对话框。

Answer 1

当它是 JDialog 时，事件来自两个不同的源。我更新了您的窗口关闭方法以提供如下堆栈跟踪:

private void formWindowClosed(java.awt.event.WindowEvent evt) {
    Exception e = new Exception();
    e.printStackTrace();
    System.out.println("formWindowClosed");
}

您可以在堆栈跟踪中判断事件的起源: java.awt.AWTEventMulticaster.windowClosed 和另一个来自 java.awt.Window.processWindowEvent。希望这会有所帮助。

全堆栈输出:

formWindowClosing : Are you sure you want to quit?
java.lang.Exception
    at JavaApplication1.formWindowClosed(JavaApplication1.java:25)
    at JavaApplication1.access$0(JavaApplication1.java:24)
    at JavaApplication1$1.windowClosed(JavaApplication1.java:10)
    at java.awt.AWTEventMulticaster.windowClosed(Unknown Source)
    at java.awt.Window.processWindowEvent(Unknown Source)
    at javax.swing.JDialog.processWindowEvent(Unknown Source)
    at java.awt.Window.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$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)
formWindowClosed
java.lang.Exception
    at JavaApplication1.formWindowClosed(JavaApplication1.java:25)
    at JavaApplication1.access$0(JavaApplication1.java:24)
    at JavaApplication1$1.windowClosed(JavaApplication1.java:10)
    at java.awt.Window.processWindowEvent(Unknown Source)
    at javax.swing.JDialog.processWindowEvent(Unknown Source)
    at java.awt.Window.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$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)
formWindowClosed