binding navigator + binding source

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C#

i a using a binding source let it be a binding source for table called Doctors(table in datacontext)
and let its name DoctorsBindingSource
and iam using a binding navigator which is linked to this binding source
i have a text field bound to DoctorsBindingSource.FirstName

my problem that i want to know that some one edits this text field and i handle that in the event validated
but when we open the form validated event is handled as the result of DoctorsBindingSource.CurrentChanged Handling
i want something to refer me (maybe bindingSource event or bindingnavigator event)that text box validated event is handled now when binding occurs
or it is handled when binding finsihed (normal state)
has any idea