title: UWP FindName return null
body: <p>I have an UWP app with a MainPage containing a SplitView called Splitview :</p>
  
  <pre><code>&lt;SplitView x:Name="SplitView" ...&gt;
  </code></pre>
  
  <p>In this SplitView, i have a usercontrol containing a ListView for navigation, when a ListViewItem is clicked, i navigate to another page but i want to close SplitView's pane before navigate. So in my usercontrol code behind in ListeView itemclick event i access parent frame and then trying to use FindName for access SplitView and close it :</p>
  
  <pre><code>var parentPage = ((Frame)Window.Current.Content);
  if (parentPage != null)
  {
      SplitView splitview = (SplitView)parentPage.FindName("SplitView");
      splitview.IsPaneOpen = false;
  }
  </code></pre>
  
  <p>parentPage have a nice reference to MainPage, but this line :</p>
  
  <pre><code>SplitView splitview = (SplitView)parentPage.FindName("SplitView");
  </code></pre>
  
  <p>always return null. Would I have missed Something ?</p>
  
  <p>Thanks in advance for your help,</p>
  
  <p>Regards</p>