Add serial number/Line num on Form [AX 2012]

Code for Serial number and write bellow code on Form Data source 
> Create method 

public void create(boolean _append = true)
{
    Table                     table;
    RefRecId                conter;

    super(_append);

    select count(RecId) from table;

    if (!table.RecId)
    table.SerialNo += 1;
    else
    table.SerialNo = table.RecId + 1;

    table_ds.refresh();
}

Happy DAXing :-)