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...
