/// <summary>
 /// Get the index of the next item that has not yet been materialized in the nominated fill direction. Returns null if there are no more available items in the source.
 /// </summary>
 protected IndexPath?GetNextUnmaterializedItem(GeneratorDirection fillDirection, IndexPath?currentMaterializedItem)
 {
     return(XamlParent?.GetNextItemIndex(currentMaterializedItem, fillDirection == GeneratorDirection.Forward ? 1 : -1));
 }
 /// <summary>
 /// Get the index of the next item that has not yet been materialized in the nominated fill direction. Returns null if there are no more available items in the source.
 /// </summary>
 protected Uno.UI.IndexPath?GetNextUnmaterializedItem(GeneratorDirection fillDirection, Uno.UI.IndexPath? currentMaterializedItem)
 {
     // TODO: adjust for reordering
     return(XamlParent?.GetNextItemIndex(currentMaterializedItem, fillDirection == GeneratorDirection.Forward ? 1 : -1));
 }