title: The type or namespace name 'Window' does not exist in the namespace 'System.Windows'
body: <p>I am trying to write an extension method for the WPF Window class.  I am doing it in a class library project in my solution, so that I can use it in all my projects in the solution.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  using System.Windows;
  
  namespace ExtensionMethods
  {
      public static class MyExtensions
      {
          public static void ResizeToPrimaryScreenWorkingArea(this System.Windows.Window w)
          { 
          }
      }
  }
  </code></pre>
  
  <p>When I try to compile this, I get the following error:</p>
  
  <blockquote>
    <p>The type or namespace name 'Window' does not exist in the namespace
    'System.Windows'</p>
  </blockquote>
  
  <p>Yes, I DID add references to System.Windows and System.Windows.Forms in my class library project, and they are showing under References in the project in Solution Explorer.</p>
  
  <p>What am I doing wrong?</p>