title: Xamarin Forms - SelectionChangedCommand not firing for CollectionView
body: <p>The code below shows a simple example of a CollectionView.  I am not receiving the event for the SelectionChangedCommand.  Can someone see what I am doing wrong?</p>
  
  <p>btw, the complete source for this can be found on GitHub <a href="https://github.com/JohnLivermore/XamarinFormsControlDemo" rel="noreferrer">here</a>.</p>
  
  <p><strong>MainPage.xaml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt;
  &lt;ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                   xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                   xmlns:local="clr-namespace:ControlDemo"
                   x:Class="ControlDemo.MainPage"&gt;
  
      &lt;StackLayout&gt;
          &lt;CollectionView SelectionMode ="Single"
                          ItemsSource="{Binding Tags}"
                          SelectionChangedCommand="{Binding SelectedTagChanged}"&gt;
              &lt;CollectionView.ItemTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;StackLayout&gt;
                          &lt;Label Text="{Binding .}" /&gt;
                      &lt;/StackLayout&gt;
                  &lt;/DataTemplate&gt;
              &lt;/CollectionView.ItemTemplate&gt;
          &lt;/CollectionView&gt;
      &lt;/StackLayout&gt;
  
  &lt;/ContentPage&gt;
  </code></pre>
  
  <p><strong>MainPageModel.cs</strong></p>
  
  <pre><code>public class MainPageModel : FreshBasePageModel
  {
      public override void Init(object initData)
      {
          Tags = new List&lt;string&gt;() { "A", "B", "C" };
          base.Init(initData);
      }
  
      public List&lt;string&gt; Tags { get; set; }
  
      public Command SelectedTagChanged
      {
          get
          {
              return new Command(() =&gt;
              {
              });
          }
      }
  }
  </code></pre>