title: MVVM Tabcontrol change tab
body: <p>I am developing an mvvm app with wpf. A requirement just got added on to block the user from changing tabs if a textbox has text. </p>
  
  <p>What is the best way to do this completely in the viewmodel? I don't know how to block a tabitem because there is no dependencyobject command in the tabcontrol to tie into, do i need to roll my own tabcontrol and build an ICommand around the SelectionChanged event?</p>
  
  <p>Should I simply (eegad..don't say it) put code in the code behind of the view in the SelectionChanged event?</p>
  
  <p>Do I have an alternative that I haven't thought of?</p>