/// <summary>
/// Gets maximal selected index.
/// </summary>
/// <returns></returns>
protected virtual int GetMaxSelectedIndex()
{
if (CollectionView == null)
{
return(-1);
}
var selectedList = CollectionView
.AsParallel()
.OfType <TItem>()
.Where(x => x.IsSelected)
.ToList();
if (selectedList.Count == 0)
{
return(-1);
}
var maxSelectedIndex = CollectionView.OfType <TItem>().ToList().IndexOf(selectedList[selectedList.Count - 1]);
return(maxSelectedIndex);
}