title: Calling method of UserControl from ViewModel with Caliburn.Micro
body: <p>I'm writing a ViewModel-first MVVM application using Caliburn.Micro
  My View contains a 3rd party UserControl that implements a Method I want/need to call from the associated ViewModel. How do I do that while still upholding the MVVM principles?</p>
  
  <p>There exists an old <a href="https://stackoverflow.com/questions/4662894/calling-method-of-map-control-with-caliburn-micro-and-wp7">thread</a> here on SO where a similar question is asked in a more specific context. I would appreciate it if someone could flesh-out the approaches suggested there a bit.</p>
  
  <p>Approach one suggests that the View could subscribe to an IEventAggregator message. But wouldn't I have to use the code behind file to do that? (I thought that was a big no no in MVVM)</p>
  
  <p>Regarding approach two, I have no idea how to do that. And regarding approach three, thats what I tried first but somehow I didn't quite get it to work.</p>