How to keep the Text of a Read only TextBox after PostBack()?

Question

I have an ASP.NET TextBox and I want it to be ReadOnly. (The user modify it using another control)

But when there is a PostBack()

Answer 1

txtStartDate.Attributes.Add("readonly", "readonly"); on pageload in the best of the best solutions ,instead or Javascripts,hidden variables,cache,cookies,sessions & Caches.