title: Xamarin.Forms - ListView does not update when data changes
body: <p><strong>Problem: Data changes but ListView does not update</strong></p>
  
  <p>I have a ListView whose ItemsSource is set to</p>
  
  <pre><code>&lt;ListView ItemsSource="{Binding ContactsGrouped}" 
  </code></pre>
  
  <p>On click of a button I update the query to only return records that contain the letters "Je". I can see that the right thing is being returned, and that ContactsGrouped is being updated, but the UI does not change.</p>
  
  <pre><code>public ObservableCollection&lt;Grouping&lt;string, Contact&gt;&gt; ContactsGrouped { get; set; }
  </code></pre>
  
  <p>where Grouping looks like this:</p>
  
  <pre><code>public class Grouping&lt;K, T&gt; : ObservableCollection&lt;T&gt;
  {
      public K Key { get; private set; }
  
      public Grouping ( K key, IEnumerable&lt;T&gt; items )
      {
          Key = key;
          foreach ( var item in items )
              this.Items.Add( item );
      }
  }
  </code></pre>
  
  <p>Given that I'm using ObservableCollections, I'd expect the list to redraw. Am I missing something obvious?</p>