Using C# to auto add item, double entries for unknown reason

Question

Using Code if a condition is met to search for a similar product code, by trimstart, and then call a method to add that product to inventory list. Unfortunately it is causing a double addition so that the product is added twice.

If I use only the line of code for the List output to a GridView it displays one entry normally.

if (item.Name.StartsWith("D"))
{
    string name = item.Name.TrimStart('D');
    List<Item> dvd = items.SelectByName(name);
    foreach (Item item2 in dvd)
    {
        Class.AddItem(item2.Id, item2.Id2, item2.Name);
    }
}

Answer 1

Can you check in your foreach, right before you AddItem, if the item already exisits in that class? If no, add, if yes, continue.

Answer 2

Here is some pseudo that you could try to add some validation before adding the item to the list:

if !the_list.Contains(the_name)
   the_list.Add(item)