WPF PopupNonTopmost重写

之前做WPF遇到问题，在网上找到的一个类

     public class PopupNonTopmost : System.Windows.Controls.Primitives.Popup
     {
         public static DependencyProperty TopmostProperty = Window.TopmostProperty.AddOwner(
         typeof(PopupNonTopmost),
         new FrameworkPropertyMetadata(false, OnTopmostChanged));

         public bool Topmost
         {
             get { return (bool)GetValue(TopmostProperty); }
             set { SetValue(TopmostProperty, value); }
         }

         private static void OnTopmostChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
         {
             (obj as PopupNonTopmost).UpdateWindow();
         }

         protected override void OnOpened(EventArgs e)
         {
             UpdateWindow();
         }

         private void UpdateWindow()
         {
             var hwnd = ((HwndSource)PresentationSource.FromVisual(this.Child)).Handle;
             RECT rect;

             if (GetWindowRect(hwnd, out rect))
             {
                 SetWindowPos(hwnd, Topmost ? - : -, rect.Left, rect.Top, (int)this.Width, (int)this.Height, );
             }
         }

         #region P/Invoke imports & definitions

         [StructLayout(LayoutKind.Sequential)]
         public struct RECT
         {
             public int Left;
             public int Top;
             public int Right;
             public int Bottom;
         }

         [DllImport("user32.dll")]
         [return: MarshalAs(UnmanagedType.Bool)]
         private static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);

         [DllImport("user32", EntryPoint = "SetWindowPos")]
         private static extern int SetWindowPos(IntPtr hWnd, int hwndInsertAfter, int x, int y, int cx, int cy, int wFlags);

         #endregion
     }