AutoLoading more content when you scroll to the bottom of a ListBox in WP7 (Windows Phone 7)

I've just implemented this for Overflow7.

The approach I took was similar to http://blog.slimcode.com/2010/09/11/detect-when-a-listbox-scrolls-to-its-end-wp7/

However, instead of using a Style I did the hook up in code.

Basically derived my parent UserControl from:

     public class BaseExtendedListUserControl : UserControl
 {
     DependencyProperty ListVerticalOffsetProperty = DependencyProperty.Register(
       "ListVerticalOffset",
       typeof(double),
       typeof(BaseExtendedListUserControl),
       new PropertyMetadata(new PropertyChangedCallback(OnListVerticalOffsetChanged)));
 
    private ScrollViewer _listScrollViewer;
 
    protected void EnsureBoundToScrollViewer()
     {
         if (_listScrollViewer != null)
             return;
 
        var elements = VisualTreeHelper.FindElementsInHostCoordinates(new Rect(0,0,this.Width, this.Height), this);
 
        _listScrollViewer = elements.Where(x => x is ScrollViewer).FirstOrDefault() as ScrollViewer;
 
        if (_listScrollViewer == null)
             return;
 
        Binding binding = new Binding();
         binding.Source = _listScrollViewer;
         binding.Path = new PropertyPath("VerticalOffset");
         binding.Mode = BindingMode.OneWay;
         this.SetBinding(ListVerticalOffsetProperty, binding);
     }
 
    public double ListVerticalOffset
     {
         get { return (double)this.GetValue(ListVerticalOffsetProperty); }
         set { this.SetValue(ListVerticalOffsetProperty, value); }
     }
 
    private static void OnListVerticalOffsetChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
     {
         BaseExtendedListUserControl control = obj as BaseExtendedListUserControl;
         control.OnListVerticalOffsetChanged();
     }
 
    private void OnListVerticalOffsetChanged()
     {
         OnListVerticalOffsetChanged(_listScrollViewer);
 
    }
 
    protected virtual void OnListVerticalOffsetChanged(ScrollViewer s)
     {
         // do nothing
     }
 }
 

this then meant that in the user control itself I could just use:

         protected override void OnListVerticalOffsetChanged(ScrollViewer viewer)
     {
         // Trigger when at the end of the viewport
         if (viewer.VerticalOffset >= viewer.ScrollableHeight)
         {
                 // actually do the load here!
         }
     }
 
    private void ListBox1_ManipulationCompleted(object sender, ManipulationCompletedEventArgs e)
     {
         EnsureBoundToScrollViewer();
     }
 

The "hacky" thing here was that I had to use ListBox1_ManipulationCompleted and VisualTreeHelper to find my ScrollViewer - I'm sure there are better ways...