title: determine a textbox's previous value in its lost focused event? WPF
body: <p>I have a textbox and have an onlostfocus event on it.</p>
  
  <p>Inside the lostfocus method, is there a way I can determine if the user has actually changed the value in it?
  i.e how do i get hold of any previous value in it?</p>
  
  <p>Thanks</p>