public PaginatedList(IQueryable <T> allItems, int pageIndex, int itemsPerPage)
{
CoreValidator.ThrowIfNotPositive(itemsPerPage);
this.TotalPages = this.CalculateTotalPages(allItems, itemsPerPage);
this.PageIndex = this.GetValidPageIndex(pageIndex);
this.data = this.GetPaginatedData(allItems, pageIndex, itemsPerPage);
}