wpf Popup控件最大化(全屏)

void MaxPopupCtrl(System.Windows.Controls.Primitives.Popup popupCtrl)
        {
            if (popupCtrl == null)
            {
                return;
            }
            popupCtrl.Width = 0;
            popupCtrl.Height = 0;
            popupCtrl.IsOpen = true;
            popupCtrl.IsOpen = false;
            Rect rtWnd = new Rect(0, 0, SystemParameters.PrimaryScreenWidth, SystemParameters.PrimaryScreenHeight);
            DependencyObject parent = popupCtrl.Child;
            do
            {
                parent = VisualTreeHelper.GetParent(parent);
                if (parent != null && parent.ToString() == "System.Windows.Controls.Primitives.PopupRoot")
                {
                    var element = parent as FrameworkElement;
                    element.Width = SystemParameters.PrimaryScreenWidth;
                    element.Height = SystemParameters.PrimaryScreenHeight;
                    rtWnd = new Rect(0, 0, element.Width, element.Height);
                    popupCtrl.PlacementRectangle = rtWnd;
                    break;
                }
            }
            while (parent != null);
            //popupCtrl.PlacementTarget = mainWnd;
            popupCtrl.IsOpen = true;
        }