使用MouseDown事件，你可以检查事件是否在弹出窗口之外引发。然后你可以关闭弹出窗口。

public MainWindow()
        {
            InitializeComponent();

            var wndPpList = new Window()
            {
                SizeToContent = SizeToContent.WidthAndHeight,
                WindowStyle = WindowStyle.None,
                ShowInTaskbar = false,
                BorderBrush =  Brushes.Cyan,
                BorderThickness = new Thickness(3),
            };
            wndPpList.Show();

            // Handle the mouse down event of the application window
            Application.Current.MainWindow.MouseDown += (s, e) =>
            {
                if (!wndPpList.IsMouseOver)
                {
                    wndPpList.Close();
                }
            };
        }

如果你需要触发事件超过一次，你需要注册和注销它正确.这是一个按钮打开弹出窗口的例子.然而，如果你打开两个弹出窗口在同一时间，你会得到problems.所以你应该禁用按钮，而弹出显示或使用一些其他机制，只显示一个弹出窗口.

public partial class MainWindow : Window
    {
        private MouseButtonEventHandler windowMouseDownHandler;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
        {
            UnregisterMouseDownEvent();
            var wndPpList = new Window()
            {
                SizeToContent = SizeToContent.WidthAndHeight,
                WindowStyle = WindowStyle.None,
                ShowInTaskbar = false,
                BorderBrush = Brushes.Cyan,
                BorderThickness = new Thickness(3),
            };
            wndPpList.Show();

            windowMouseDownHandler = (s, e) =>
            {
                if (!wndPpList.IsMouseOver)
                {
                    wndPpList.Close();
                }
            };
            // Register the event handler function
            Application.Current.MainWindow.MouseDown += windowMouseDownHandler;
        }

        private void UnregisterMouseDownEvent()
        {
           
            if (windowMouseDownHandler != null)
            {
                Application.Current.MainWindow.MouseDown -= windowMouseDownHandler;
            }
           
        }