public void FillDG(DateTime?firstDay, DateTime?lastDay)
{
this.dgReports.Items.Clear();
List <RentedBookList> rentedBookLists = dr.FillReportsList(firstDay, lastDay);
foreach (RentedBookList rentedBookList in rentedBookLists)
{
this.dgReports.Items.Add(rentedBookList);
}
}