[ DllImport ( "USER32.DLL" ) ]public static extern int GetSystemMenu(int hwnd, int bRevert);[ DllImport ( "USER32.DLL" ) ]public static extern int RemoveMenu(int hMenu, int nPosition, int wFlags);/// <summary>/// 返回值，非零表示成功，零表示失敗。/// </summary>/// <param name="iHWND">窗口的句柄</param>/// <returns>是否成功</returns>public int RemoveXButton(int iHWND){  int iSysMenu;  const int MF_BYCOMMAND = 0x400; //0x400-關閉  iSysMenu = GetSystemMenu(this.Handle.ToInt32(), 0);  return RemoveMenu(iSysMenu, 6, MF_BYCOMMAND);}private void Form1_Load(object sender, EventArgs e){    //通過函數返回值就可以判斷目的是否達到，在構造函數里面可以這樣判斷：    int iReturn = RemoveXButton(this.Handle.ToInt32());    if (iReturn == 0) //返回值非零表示成功，零表示失敗。    {      MessageBox.Show("Error!");    }    else    {      MessageBox.Show("Success!");    }}