title: Cannot Import System.Windows.Controls
body: <p>I am trying to use <code>System.Windows.Controls.TextChangedEventArgs</code>, but I cannot import <code>System.Windows.Controls</code>. When I try to add a reference, <code>System.Windows.Controls</code> is not one of the assemblies that I can select. </p>
  
  <p>Does anyone know how to resolve the issue?</p>