using Master Detail datalist

Hi I have a master detail datalist the detail deta list shows the component relatet to master product in shopping cart I want to edit items in master data list and in detail data list (Dtl_Component) is my detail data list I try this code but becouse my detaile data grid dosent make at this time I have an error Object reference not set to an instance of an object.Dtl_Component.EditItemIndex = -1; public void Dtl_Component_CancelCommand(Object Sender, DataListCommandEventArgs e) { Dtl_Component.EditItemIndex = -1; Dtl_Component("All_Item"); } do you know any idea or any sample how can I edit the detail datalist or datagrid? Regards...Mahsa