>>Most of the time my column are readonly, only under cirtain conditions I allow to edit text content in a column. I'd like to fire Valid method only in cases, when something was actually changed in a grid textbox, how can I achieve this functionality?
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>More information please, what are the special cases that the controls are editable?

Ok, I do some calculations on the field, e.g. calculate APN, for example. If my routine indicates "BAD" Apn or Duplicate APNs, I make these records to be editable. Otherwise all grid controls are read-only. Only if I have them editable (BAD or duplicates) I want to perform valid, if I really typed something in these fields.