title: How to center the picture list in CollectionView / Xamarin
body: <p>I have simple CollectionView to show vertically pictures.
  The CollectionView is binded to string list.
  I want to show the pictures in the middle of the screen. But they come always at the top of the screen.
  Here is my xaml:</p>
  
  <pre><code>&lt;CollectionView ItemsSource="{Binding Pictures}" HorizontalOptions="Center" VerticalOptions="Center"&gt;
       &lt;CollectionView.ItemTemplate&gt;
           &lt;DataTemplate&gt;
               &lt;StackLayout Padding="10" HorizontalOptions="Center" VerticalOptions="Center"&gt;
                   &lt;Image Source="{Binding .}"/&gt; 
               &lt;/StackLayout&gt; 
           &lt;/DataTemplate&gt;
       &lt;/CollectionView.ItemTemplate&gt;
  &lt;/CollectionView&gt;
  </code></pre>
  
  <p>Important: the count of the pictures is not always the same.</p>
  
  <p><a href="https://i.stack.imgur.com/Qc64m.jpg" rel="nofollow noreferrer">Image</a></p>
  
  <p><a href="https://i.stack.imgur.com/xf1Fk.jpg" rel="nofollow noreferrer">Screen Shot</a></p>