title: ItemContainerGenerator.ContainerFromItem() returns null?
body: <p>I'm having a bit of weird behavior that I can't seem to work out.  When I iterate through the items in my ListBox.ItemsSource property, I can't seem to get the container?  I'm expecting to see a ListBoxItem returned, but I only get null.</p>
  
  <p>Any ideas?</p>
  
  <p>Here's the bit of code I'm using:</p>
  
  <pre><code>this.lstResults.ItemsSource.ForEach(t =&gt;
      {
          ListBoxItem lbi = this.lstResults.ItemContainerGenerator.ContainerFromItem(t) as ListBoxItem;
  
          if (lbi != null)
          {
              this.AddToolTip(lbi);
          }
      });
  </code></pre>
  
  <p>The ItemsSource is currently set to a Dictionary and does contain a number of KVPs.</p>