Mdiフォームカスタマーエリアの枠線なし表示

  #region   API
        // Win32 Constants
        private const int GWL_STYLE = -16;
        private const int GWL_EXSTYLE = -20;

        private const int WS_BORDER = 0x00800000;
        private const int WS_EX_CLIENTEDGE = 0x00000200;

        private const uint SWP_NOSIZE = 0x0001;
        private const uint SWP_NOMOVE = 0x0002;
        private const uint SWP_NOZORDER = 0x0004;
        private const uint SWP_NOREDRAW = 0x0008;
        private const uint SWP_NOACTIVATE = 0x0010;
        private const uint SWP_FRAMECHANGED = 0x0020;
        private const uint SWP_SHOWWINDOW = 0x0040;
        private const uint SWP_HIDEWINDOW = 0x0080;
        private const uint SWP_NOCOPYBITS = 0x0100;
        private const uint SWP_NOOWNERZORDER = 0x0200;
        private const uint SWP_NOSENDCHANGING = 0x0400;


        // Win32   
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern int GetWindowLong(IntPtr hWnd, int Index);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern int SetWindowLong(IntPtr hWnd, int Index, int Value);

        [DllImport("user32.dll", ExactSpelling = true)]
        private static extern int SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter,
            int X, int Y, int cx, int cy, uint uFlags);

        #endregion


        /// <summary>
        ///      ，               
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void MainForm_Shown(object sender, EventArgs e)
        {
            //  mdi   
            MdiClient mdiClient = null;
            for (int i = 0; i < this.Controls.Count; i++)
            {

                mdiClient = this.Controls[i] as MdiClient;
                if (mdiClient != null)
                {
                    //    mdi   
                    //         
                    int style = GetWindowLong(mdiClient.Handle, GWL_STYLE);
                    int exStyle = GetWindowLong(mdiClient.Handle, GWL_EXSTYLE);
                    style &= ~WS_BORDER;
                    exStyle &= ~WS_EX_CLIENTEDGE;

                    //   win32    
                    SetWindowLong(mdiClient.Handle, GWL_STYLE, style);
                    SetWindowLong(mdiClient.Handle, GWL_EXSTYLE, exStyle);

                    //      
                    SetWindowPos(mdiClient.Handle, IntPtr.Zero, 0, 0, 0, 0,
                        SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER |
                        SWP_NOOWNERZORDER | SWP_FRAMECHANGED);
                    UpdateStyles();
                    break;
                }
            }
        }