How control when textBox.Text is changed when currentItem in bindingSource is changed

I have dataGridView bound to some bindingSource. In textBox I display currentItem values. 
I want this behaviour:
When user click MoveNext on bindingNavigator(or previous, doesn't matter), I want first display simple dialog if he want to save changes and then update all textBoxes with this new selected item values from bindingSource.
I have tried PositionChanged event, but it changes text before dialog shows.

Is there any way so that user first see Dialog and after he confirm/denied saving changes, he see new values is textBox? I've also tried to change textBox update mode to "OnPropertyChange", but result is the same.