Enable/Disable and Edit Form Control Fields in Ax 2012

Enable/Disable  and  Edit  Form Control Fields .

ledgerJournalTrans_DS.object(fieldnum(LedgerJournalTrans, TransDate)).allowEdit(false);
ledgerJournalTrans_DS.object(fieldnum(LedgerJournalTrans, TransDate)).Enable(false);
ledgerJournalTrans_DS.object(fieldnum(LedgerJournalTrans, TransDate)).Enable(true);

// validate record using exist method------------------------------------

if(!LedgerJournalTable::exist(JourNo))
 {
          error(strfmt("ERROR: Invalid Journal Number !!!",JourNo));
          return false;
}