Thanks dudes for nice suggestion but my problem is still there i have a dropdownlist which is populated from Province table.In GridView SelectedIndexChanging When i select the row then it fill all the texboxes and dropdownlist.Problm is that if in Province field is null then it throws exception.
'ddlstate' has a SelectedValue which is invalid because it does not exist in the list of items.
Parameter name: value.
On Populating DrodownList i use this approch.
ddlstate.Items.Insert(0, "--Select Province--");
GridView Code SelectedIndexChanging