做項目中間遇到了MDI窗體內邊框的問題，經過苦苦尋找，最終得到了解決方案

在Main窗體中調用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_NOACTIVATE = 0x0010;
        private const uint SWP_FRAMECHANGED = 0x0020;
        private const uint SWP_NOOWNERZORDER = 0x0200;


        // Win32 方法    
        [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);


獲取到API後在Form_Load事件中加入如下代碼  

  //獲取mdi客戶區    
            for (int i = 0; i < this.Controls.Count; i++)
            {
                var mdiClientForm = this.Controls[i] as MdiClient;
                if (mdiClientForm == null) continue;
                // 找到了mdi客戶區    
                // 取得客戶區的邊框    
                int style = GetWindowLong(mdiClientForm.Handle, GWL_STYLE);
                int exStyle = GetWindowLong(mdiClientForm.Handle, GWL_EXSTYLE);
                style &= ~WS_BORDER;
                exStyle &= ~WS_EX_CLIENTEDGE;

                // 調用win32設定樣式    
                SetWindowLong(mdiClientForm.Handle, GWL_STYLE, style);
                SetWindowLong(mdiClientForm.Handle, GWL_EXSTYLE, exStyle);

                // 更新客戶區    
                SetWindowPos(mdiClientForm.Handle, IntPtr.Zero, 0, 0, 0, 0,
                    SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER |
                    SWP_NOOWNERZORDER | SWP_FRAMECHANGED);
                UpdateStyles();
                break;
            }

重新運行程序，OK

Winform下去除MDI窗體邊框