How to use a field of a form in Dynamics AX

First of all you have to select this field and set Autodecalartion proprety toYes.

  Then, in your code use this code :

  Emplid                            employeeId;

 Str                               _value;  

 element.design().controlName(identifierStr(emplid));

 employeeId = emplid.text();

But if you want to use it as an Str use this :

 _value= emplid.valueStr();