java - 窗口焦点事件的意外行为

Question

我正在使用 Swing 创建应用程序，但遇到了问题。我想处理 focusLost() 和 focusGained() 事件，但我认为我的代码有问题。

我有以下测试代码:

addWindowFocusListener(new WindowFocusListener() {
    @Override
    public void windowLostFocus(WindowEvent e) {
        System.out.println("Lost!");
        System.out.println(e.toString());
    }

    @Override
    public void windowGainedFocus(WindowEvent e) {
        System.out.println("Gained!");
        System.out.println(e.toString());
    }
});

而且，当我激活窗口时，应用似乎一次处理了 2 个事件:

Gained!
java.awt.event.WindowEvent[WINDOW_GAINED_FOCUS,opposite=null,oldState=0,newState=0] on frame0
Lost!
java.awt.event.WindowEvent[WINDOW_LOST_FOCUS,opposite=null,oldState=0,newState=0] on frame0

而且，当我停用窗口时，程序什么也不打印。

还有更有趣的事情。当我打开一个属于我的应用程序的新 JFrame 时，事件系统正常工作，即使我关闭了第二个 Window。

我只是不知道为什么会这样。请帮忙。

系统规范:

• 操作系统:Ubuntu 12.04 x86_64
  
• JVM:OpenJDK 7

m4tx@m4tx-EP35-DS4:~$ java -version
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=lcd
java version "1.7.0_03"
OpenJDK Runtime Environment (IcedTea7 2.1.1pre) (7~u3-2.1.1~pre1-1ubuntu3)
OpenJDK 64-Bit Server VM (build 22.0-b10, mixed mode)

Answer 1

嗯，我看不出你的代码有什么问题；所以我整理了一个快速演示，它似乎运行良好:

import java.awt.event.WindowEvent;
import java.awt.event.WindowFocusListener;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class WindowEventDemo extends JFrame implements WindowFocusListener {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new WindowEventDemo("Window Event Demo").setVisible(true);
            }
        });
    }

    public WindowEventDemo(String name) {
        super(name);
        addWindowFocusListener(this);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 300);
    }

    @Override
    public void windowGainedFocus(WindowEvent e) {
        System.out.println("WindowFocusListener method called: windowGainedFocus.");
    }

    @Override
    public void windowLostFocus(WindowEvent e) {
        System.out.println("WindowFocusListener method called: windowLostFocus.");
    }
}

启动时打印:

WindowFocusListener method called: windowGainedFocus.

当窗口被最小化，或者鼠标在屏幕上的其他地方被点击时，除了打印JFrame:

WindowFocusListener method called: windowLostFocus.