WP7 Auto Grow ListBox upon reaching the last item

Question

I\'m trying to achieve an effect where more items are appended to the list when the user scrolls down to the last item. I haven\'t found a way to determine if the user has s

Answer 1

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)
        {
            if (MoreClick != null)
            {
                MoreClick(this, new RoutedEventArgs());
            }
        }
    }

    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...