BEGIN_MESSAGE_MAP(CLeftDlgBar, CDialogBar)
ON_UPDATE_COMMAND_UI(IDC_BUTTON1,OnUpdateButton1)
END_MESSAGE_MAP()
void CLeftDlgBar::OnUpdateButton1(CCmdUI* pCmdUI)
{
pCmdUI->Enable(TRUE);
//using pCmdUI->SetText you can set the button text too
}