How to validate user input on a CEdit?

Hi, I want to validate user input on a CEdit.

If users click OK or Enter and the CEdit still blank, then I must raise
error dialog message to current user.

I have done this way below but it did not work:

By the way, I don't know how to handle the keydown event to catch if user
press Enter. Because I thought that the CWnd has handled it automatically
since if the focus is on the CEdit and I press Enter key, the dialog will
automatically closed.

How to handle the KeyDown event?

void CEditDlg::OnOK()
{
    // TODO: ???????????????????????????????????????????????????????????????????????????
    UpdateData( TRUE );
    if ( m_edtFujiCode != "" )
    {
        if ( m_stcTOACode.CompareNoCase( m_pItemData->m_sName ) == 0 )
        {
            m_pItemData->m_sFujiCode = m_edtFujiCode;
            if ( m_sTempFujiVal.CompareNoCase( m_edtFujiCode ) != 0 )
                m_pItemData->m_bItemSave = TRUE;
            else
                m_pItemData->m_bItemSave = FALSE;
        }
    }
    else
    {
        AfxMessageBox( "????????????????????????????????????????????????????????????" );
        GetDlgItem( IDC_FUJICODE )->SetFocus();
    }
    CDialog::OnOK();
}

Thank you very much.