title: check if value in textbox is valid
body: <p>I have a textbox with a validator that permits only integer values. How do I check if text in my textbox represents a correct integer value without checking the text itself?</p>
  
  <p>I am using Prism MVVM so I would like to hear some solution like "bind a validator property to your viewmodel/model code", but a generic WPF solution is also fine.</p>
  
  <p>The problem is that I can't get the incorrect value in my model / viewmodel. If the value is incorrect, then the underlying binded property doesn't get set.</p>