TextBox TextChange Event

[sunilthk]

Hi All,
I want to know how the TextBox control knows that it's data has been
changed, since it is able to detect changes and fires TextChange event
if the data in the TextBox has been changed. I know that TextBox class
implements IPostBackDataHandler interface which defines a method
LoadPostData(string postDataKey,NameValueCollection postCollection)
the postCollection keeps the posted data for each web control. How
ASP.NET fills this postCollection objects, i thought that ASP.NET uses
view state to get posted values, but i set EnableViewState property of
the text box then also the text changed event is firing.
Please let me know how this happens.
Thanks
Sunil