title: Allow only numeric entry in WPF Text Box
body: <p>I will like to validate user entry to ensure they are integers. How can I do it? I thought of using <code>IDataErrorInfo</code> which seems like the "correct" way to do validation in WPF. So I tried implementing it, in my ViewModel.</p>
  
  <p>But the thing is my text box is bound to an integer field, and there isn't any need to validate if an <code>int</code> is an <code>int</code>. I noticed that WPF automatically adds a red border around the textbox to notify the user of the error. The underlying property doesn't change to an invalid value. But I would like to notify the user of this. How can I do it?</p>