How to replace list item in best way

Question

if (listofelements.Contains(valueFieldValue.ToString()))
{
    listofelements[listofelements.IndexOf(valueFieldValue.ToString())] = value.ToString();
}

Answer 1

i find best for do it fast and simple

1. find ur item in list

   var d = Details.Where(x => x.ProductID == selectedProduct.ID).SingleOrDefault();
   

2. make clone from current

   OrderDetail dd = d;
   

3. Update ur clone

   dd.Quantity++;
   

4. find index in list

   int idx = Details.IndexOf(d);
   

5. remove founded item in (1)

     Details.Remove(d);
   

6. insert

    if (idx > -1)
         Details.Insert(idx, dd);
     else
         Details.Insert(Details.Count, dd);