C# Kapat butonunu pasifleştirmek

private const int SC_CLOSE = 0xF060;
          private const int MF_GRAYED = 0x1;
 
          [DllImport("user32.dll")]
          private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);
 
          [DllImport("user32.dll")]
          private static extern int EnableMenuItem(IntPtr hMenu, int wIDEnableItem, int wEnable);
 
          private void Form1_Load(object sender, System.EventArgs e)
          {
               EnableMenuItem(GetSystemMenu(this.Handle, false), SC_CLOSE, MF_GRAYED);
          }