WindowListener 无法按预期工作 [英] WindowListener does not work as expected

问题描述

I want my GUI to make some checks when a JOptionPane appears. Because I can't find any other way, I though I can do those each time the application window loses focus(its just checking a string). For that reason I added the following code on my JFrame:

appFrame.addWindowListener(new WindowAdapter() {

            @Override
            public void windowLostFocus(WindowEvent e) {
                System.out.println("Focus Lost");

            }
            @Override
            public void windowClosing(WindowEvent e) {
                //some other stuff here that work
            }
});

The window closing listener works fine. Although when the JFrame isn't focused nothing happens. Shouldn't "Focus Lost" be printed each time I switch from JFrame to some other window? Also, will this method be triggered when a JOptionPane is shown?

解决方案

I'm not going to go into why you are doing what you are doing, but it is not working as you expect for the following reason:

WindowAdapter is a convenience class so you can create one listener and register it for multiple types of events. You have only registered it for one set of events, you need to also register it for focus events via: Window.addWindowFocusListener()

WindowAdapter adapter = new WindowAdapter() {
        @Override
        public void windowLostFocus(WindowEvent e) {
            System.out.println("Focus Lost");
        }
        @Override
        public void windowClosing(WindowEvent e) {
            //some other stuff here that work
        }
    };
appFrame.addWindowListener(adapter);
appFrame.addWindowFocusListener(adapter);

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