WPF - reset ListBox scroll position when ItemsSource changes

Question

I currently have a ListBox whose ItemsSource collection is bound to a property on my viewmodel, of type IEnumerable. When that preoprty\'s reference changes, the ListBox update

Answer 1

Improved Fredrik Hedblad's answer to work with ObservableCollection:

public static class ItemsControlAttachedProperties
{
    #region ScrollToTopOnItemsSourceChange Property

    public static readonly DependencyProperty ScrollToTopOnItemsSourceChangeProperty =
        DependencyProperty.RegisterAttached(
            "ScrollToTopOnItemsSourceChange",
            typeof(bool),
            typeof(ItemsControlAttachedProperties),
            new UIPropertyMetadata(false, OnScrollToTopOnItemsSourceChangePropertyChanged));

    public static bool GetScrollToTopOnItemsSourceChange(DependencyObject obj)
    {
        return (bool) obj.GetValue(ScrollToTopOnItemsSourceChangeProperty);
    }

    public static void SetScrollToTopOnItemsSourceChange(DependencyObject obj, bool value)
    {
        obj.SetValue(ScrollToTopOnItemsSourceChangeProperty, value);
    }

    static void OnScrollToTopOnItemsSourceChangePropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        var itemsControl = obj as ItemsControl;
        if (itemsControl == null)
        {
            throw new Exception("ScrollToTopOnItemsSourceChange Property must be attached to an ItemsControl based control.");
        }

        DependencyPropertyDescriptor descriptor =
            DependencyPropertyDescriptor.FromProperty(ItemsControl.ItemsSourceProperty, typeof(ItemsControl));
        if (descriptor != null)
        {
            if ((bool) e.NewValue)
            {
                descriptor.AddValueChanged(itemsControl, ItemsSourceChanged);
            }
            else
            {
                descriptor.RemoveValueChanged(itemsControl, ItemsSourceChanged);
            }
        }
    }

    static void ItemsSourceChanged(object sender, EventArgs e)
    {
        var itemsControl = sender as ItemsControl;
        DoScrollToTop(itemsControl);

        var collection = itemsControl.ItemsSource as INotifyCollectionChanged;
        if (collection != null)
        {
            collection.CollectionChanged += (o, args) => DoScrollToTop(itemsControl);
        }
    }

    static void DoScrollToTop(ItemsControl itemsControl)
    {
        EventHandler eventHandler = null;
        eventHandler =
            delegate
            {
                if (itemsControl.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
                {
                    var scrollViewer = GetVisualChild(itemsControl);
                    scrollViewer.ScrollToTop();
                    itemsControl.ItemContainerGenerator.StatusChanged -= eventHandler;
                }
            };
        itemsControl.ItemContainerGenerator.StatusChanged += eventHandler;
    }

    static T GetVisualChild(DependencyObject parent) where T : Visual
    {
        T child = default(T);
        int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
        for (var i = 0; i < numVisuals; i++)
        {
            var v = (Visual) VisualTreeHelper.GetChild(parent, i);
            child = v as T ?? GetVisualChild(v);
            if (child != null)
            {
                break;
            }
        }
        return child;
    }

    #endregion
}