title: Binding Command of Button in AppBar does not work
body: <p>Why does the Command in the following example not execute?</p>
  
  <p>I have a named Page with an AppBar and a Button in it:</p>
  
  <pre><code>   &lt;Page
      x:Class="App13.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d" 
      x:Name="myPage"
      &gt;
      &lt;Page.BottomAppBar&gt;
          &lt;AppBar&gt;
             &lt;Button Content="OK" Command="{Binding OkCommand, ElementName=myPage}" /&gt;
          &lt;/AppBar&gt;
      &lt;/Page.BottomAppBar&gt;
  &lt;/Page&gt;
  </code></pre>
  
  <p>The Command "OkCommand" is defined in the code-behind like this (using MVVM light framework):</p>
  
  <pre><code>public RelayCommand OkCommand
  {
      get
      {
          return m_OkCommand
              ?? (m_OkCommand = new RelayCommand(
                                    async () =&gt;
                                    {
                                        await new MessageDialog("OkCommand").ShowAsync();
                                    }));
      }
  }
  </code></pre>
  
  <p>There are no binding-errors nor any other hints in the output-window that give me an idea why this does not work. 
  (Aside: if the button is placed outside the AppBar, everything works fine)</p>
  
  <p>Does anyone have an idea what is wrong here?</p>