title: Can't find reference to System.Diagnostics.Stopwatch
body: <p>I am attempting to build a simple stopwatch WPF application.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Configuration;
  using System.Data;
  using System.Linq;
  using System.Threading.Tasks;
  using System.Windows;
  using System.Diagnostics;
  
  namespace WpfApplication1
  {
  /// &lt;summary&gt;
  /// Interaction logic for App.xaml
  /// &lt;/summary&gt;
  public partial class App : Application
  {
      public stopWatch = new Stopwatch();
  
      private void startTimer()
      {
          stopWatch.Start();
          Dispatcher.BeginInvoke(DispatcherPriority.Render, new ThreadStart(ShowElapsedTime));
      }
      void ShowElapsedTime()
      {
          TimeSpan ts = stopWatch.Elapsed;
          lblTime.Text = String.Format("{0:00}:{1:00}.{2:00}", ts.Minutes, ts.Seconds, ts.Milliseconds / 10);
      }
  }
  }
  </code></pre>
  
  <p>and here</p>
  
  <p><img src="https://i.stack.imgur.com/999Bn.png" alt="enter image description here"></p>
  
  <p>I am using System.Diagnostics but for some reason I cannot access the <a href="http://msdn.microsoft.com/en-us/library/system.diagnostics.stopwatch%28v=vs.110%29.aspx" rel="nofollow noreferrer">Stopwatch</a></p>
  
  <p>and also I can't find System.Diagnostics in this Dialogue:</p>
  
  <p><img src="https://i.stack.imgur.com/PfRhi.png" alt="enter image description here"></p>
  
  <p>Why can't I use System.Diagnostics.Stopwatch and why does System.Diagnostics not appear in the references dialog?</p>