public Driver(FastVerticallyScrollingItemViewer parent, IComparer <T> comparer)
{
this._parent = parent;
this._layoutTree = new PersistentAggregatingRedBlackTree <Unique <T>, ControlData, double>(
(a1, k, v, a2) => a1 + v.Value.Type.Height + a2,
Unique <T> .MakeComparerUnique(comparer));
parent.scrollView.ViewChanged += (sender, arg) => UpdateShown();
parent.scrollView.SizeChanged += (sender, arg) => {
parent.layoutArea.Width = arg.NewSize.Width; // Warning: removing this may result in search results that drift right/left as they are manipulated by touch
UpdateShown();
};
}