[WPF疑難] 模式窗口被隱藏後重新顯示時變成了非模式窗口

現象：

大家可以試試下面這個很有趣但會帶來Defect的現象：當我們將子窗口按照ShowDialog()的方式顯示出來的時候，很明顯該窗口是模式化的（即主窗口等待該窗口的返回，主窗口將不相應用戶輸入），但如果此時將子窗口的Visibility設置成Visibility.Hidden來隱藏窗口，然後再將Visibility設置成Visibility.Visible來再次顯示子窗口，此後子窗口便是非模式的了（即主窗口和子窗口一樣相應用戶輸入）

案例：

當用戶不操作軟件達到一定的時間間隔後，軟件會隱藏該軟件當前顯示的所有窗口，並彈出“鎖定窗口”，當用戶手動解鎖後，“鎖定窗口”隱藏，其它所有窗口重新顯示出來。

對於上述案例中的窗口，如果使用設置Visibility的方式來顯示或隱藏窗口，如果被隱藏的窗口是模式對話框的化，便會在重新顯示時出現上述問題。

解決方案：

可以用一個相對簡單的方式來解決這個問題：“隱藏” 就是 "看不見”， “把窗口扔到顯示屏幕之外”就是“看不見”。（這屬於“WO，KAO"類的方案，而非”WOW，SAI“，不過卻能很好地工作。”寫軟件就是騙入“----用高科技騙人的眼睛、耳朵，寫游戲就更得會騙人了）

代碼：

public class WindowVisibilityHelper : DependencyObject
    {
        public static bool GetIsVisible(DependencyObject obj)
        {
            return (bool)obj.GetValue(IsVisibleProperty);
        }
        public static void SetIsVisible(DependencyObject obj, bool value)
        {
            obj.SetValue(IsVisibleProperty, value);
        }
        public static readonly DependencyProperty IsVisibleProperty =
            DependencyProperty.RegisterAttached("IsVisible", typeof(bool), 
            typeof(WindowVisibilityHelper), 
            new PropertyMetadata(true, IsVisiblePropertyChangedCallback));
        private static void IsVisiblePropertyChangedCallback(DependencyObject obj, 
            DependencyPropertyChangedEventArgs e)
        {
            var window = (Window)obj;
            var visible = (bool)e.NewValue;
            if (!visible)
            {
                SetWindowState(window, window.WindowState);
                if (window.WindowState == WindowState.Maximized)
                {
                    window.WindowState = WindowState.Normal;
                }
                SetWindowLocation(window, new Point(window.Left, window.Top));
                window.Left = -100000;
                window.Top = -100000;
                SetWindowIsShowInTaskBar(window, window.ShowInTaskbar);
                window.ShowInTaskbar = false;
            }
            else
            {
                window.WindowState = GetWindowState(window);
                Point loc = GetWindowLocation(window);
                window.Left = loc.X;
                window.Top = loc.Y;
                window.ShowInTaskbar = GetWindowIsShowInTaskBar(window);
                window.Activate();
                window.BringIntoView();
            }
        }
        private static Point GetWindowLocation(DependencyObject obj)
        {
            return (Point)obj.GetValue(WindowLocationProperty);
        }
        private static void SetWindowLocation(DependencyObject obj, Point value)
        {
            obj.SetValue(WindowLocationProperty, value);
        }
        private static readonly DependencyProperty WindowLocationProperty =
            DependencyProperty.RegisterAttached("WindowLocation", typeof(Point), 
            typeof(WindowVisibilityHelper), new UIPropertyMetadata(new Point()));
        private static WindowState GetWindowState(DependencyObject obj)
        {
            return (WindowState)obj.GetValue(WindowStateProperty);
        }
        private static void SetWindowState(DependencyObject obj, WindowState value)
        {
            obj.SetValue(WindowStateProperty, value);
        }
        private static readonly DependencyProperty WindowStateProperty =
            DependencyProperty.RegisterAttached("WindowState", typeof(WindowState), 
            typeof(WindowVisibilityHelper), new UIPropertyMetadata(WindowState.Normal));
        private static bool GetWindowIsShowInTaskBar(DependencyObject obj)
        {
            return (bool)obj.GetValue(WindowIsShowInTaskBarProperty);
        }
        private static void SetWindowIsShowInTaskBar(DependencyObject obj, bool value)
        {
            obj.SetValue(WindowIsShowInTaskBarProperty, value);
        }
        private static readonly DependencyProperty WindowIsShowInTaskBarProperty =
            DependencyProperty.RegisterAttached("WindowIsShowInTaskBar", typeof(bool), 
            typeof(WindowVisibilityHelper), new UIPropertyMetadata(true));
    }