C#

public class MyForm:Form<br />
{<br />
  private bool _cancelButtonClicked = false;<br />
  private void cancelbutton_clicked(..)<br />
  {<br />
    _cancelButtonClicked = true;<br />
  }<br />
  private void form_closing(..)<br />
  {<br />
     if (_cancelButtonClicked)<br />
     {<br />
        //User clicked the button with the dialog result == cancel<br />
     }<br />
     else<br />
     {<br />
        //User clicked X button to close the form<br />
     }<br />
  }<br />
}

private const int WM_SYSCOMMAND = 0x112; 
private const int SC_CLOSE = 0xF060;

protected override void WndProc(ref Message m)
{
     if (m.Msg == WM_SYSCOMMAND && m.WParam.ToInt32() == SC_CLOSE)
     {
          //do something here
     }
}

<br />
            System.Windows.Forms.ToolStripMenuItem mi = (ToolStripMenuItem)menuStrip1.Items[0];<br />
            mi.DropDownItems[0].Enabled = false;