>How can I change property (my added) of class from form of that class from some method?
>I have tried with command THIS but I didn't work (also I need explain of that command).

Just in case you missed it, THIS and THISFORM cannot be used outside of an object I.E. you can't do it in a .PRG, furthmore, THISFORM cannot be used in an object which not contained somewhere in a form.

HTH