title: How to control closing / leaving open a wpf window from ViewModel?
body: <p>I have a WPF window that is opened when the user clicks on one of the toolbar's buttons of my WPF control.</p>
  
  <p>The user has to enter some data and then press the 'OK' button. When the 'OK' button is pressed I process the data, and if the processing was successful I want to close the window, otherwise I want to display a message, but leave the window opened.</p>
  
  <p>How do I control closing / not closing the window from my ViewModel?</p>