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));

}