.Net下去掉MDI窗体内客户区的边框

      .NET下，MDI窗体内客户区的3D边框很难看，下面是我写的一个类，可以去掉这个边框：

using  System;
using  System.Runtime.InteropServices;

namespace  iUNS
{
     ///   <summary>
     ///  iuSetMdiClientBorder 的摘要说明。
     ///   </summary>
     public   class  iuSetMdiClientBorder
    {
        [DllImport( " user32.dll " , CharSet = CharSet.Auto)]
         public   static   extern   int  GetWindowLong( int  hwnd,  int  nIndex);
        [DllImport( " user32.dll " , CharSet = CharSet.Auto)]
         public   static   extern   int  SetWindowLong( int  hwnd,  int  nIndex,  int  dwNewLong);
         private   const   int  GWL_EXSTYLE  =  ( - 20 );
         private   const   int  WS_EX_CLIENTEDGE  =   0x0200 ;

         public  iuSetMdiClientBorder()
        {
             //
             //  TODO: 在此处添加构造函数逻辑
             //
        }

         ///   <summary>
         ///  设置Mdi窗口客户区是否绘制3D边框
         ///   </summary>
         ///   <param name="hWnd"> Mdi窗口的Handle </param>
         ///   <param name="showBorder"> 是否绘制3D边框 </param>
         public   static   void  SetMdiClientBorder( int  hWnd, bool  showBorder)
        {
             int  windowLong  =  GetWindowLong(hWnd,GWL_EXSTYLE);
             if (showBorder)
                windowLong  =  windowLong  &  WS_EX_CLIENTEDGE;
             else
                windowLong  =  windowLong  &   ~ WS_EX_CLIENTEDGE;
            
            SetWindowLong(hWnd, GWL_EXSTYLE, windowLong);
        }
    }
}