/// <summary>
/// Calculate the distance between this TreeViewItem and the item being
/// paged from.
/// </summary>
/// <param name="up">
/// A value indicating whether the page should be scrolled up.
/// </param>
/// <param name="element">The element being paged from.</param>
/// <param name="scrollHost">The ScrollViewer being scrolled.</param>
/// <param name="top">The top of item to start from.</param>
/// <param name="bottom">The bottom of the item to start from.</param>
/// <param name="closeEdge">
/// The distance between the top/bottom of one item to the other.
/// </param>
/// <returns>
/// A value indicating whether the scroll was handled.
/// </returns>
private static double CalculateDelta(bool up, FrameworkElement element, ScrollViewer scrollHost, double top, double bottom, out double closeEdge)
{
double elementTop, elementBottom;
element.GetTopAndBottom(scrollHost, out elementTop, out elementBottom);
if (up)
{
closeEdge = bottom - elementBottom;
return bottom - elementTop;
}
else
{
closeEdge = elementTop - top;
return elementBottom - top;
}
}