C# Foreach keep adding the same item to list

Question

I am having issues with my simple foreach. I am trying to get data from the database to my list.

IList<DeliveredTaskModel> deliveredTaskModel = new List<DeliveredTaskModel>();
// lines of code 

if (materialUsed.Count > 0)
{
    foreach (var material in materialUsed)
    {
        var deliveryModel = new DeliveredTaskModel();
        deliveryModel.Info = materialUsed[0].SubPartCode;
        deliveryModel.Description = materialUsed[0].Description;
        deliveryModel.Qty = materialUsed[0].Qty;
        deliveredTaskModel.Add(deliveryModel);
    }
}

when I set a breakpoint on the foreach. I can see that it has 4 different items in materialUsed. however, when I do this foreach, it simply adds 4x the same item to the grid.

I assume it keeps adding the same item, but why? Could someone explain?

Answer 1

You are always accessing by index zero constantly. Options to correct:

1. If you use foreach use:

   foreach (var material in materialUsed)
   {
       var deliveryModel = new DeliveredTaskModel();
       deliveryModel.Info = material.SubPartCode;
       deliveryModel.Description = material.Description;
       deliveryModel.Qty = material.Qty;
       deliveredTaskModel.Add(deliveryModel);
   }
   

2. If you use by indexer change to for-loop:

   for(int i = 0; i < materialUsed.Count, i++)
   {
       var deliveryModel = new DeliveredTaskModel();
       deliveryModel.Info = materialUsed[i].SubPartCode;
       deliveryModel.Description = materialUsed[i].Description;
       deliveryModel.Qty = materialUsed[i].Qty;
       deliveredTaskModel.Add(deliveryModel);
   }
   

3. Then it will be nicer to user property initializer:

   foreach (var material in materialUsed)
   {
       deliveredTaskModel.Add(new DeliveredTaskModel
       {
           Info = material.SubPartCode,
           Description = material.Description,
           Qty = material.Qty
       });
   }
   

4. And then using linq you can achieve it with .Select

   var deliveredTaskModel = materialUsed.Select(material => new DeliveredTaskModel
       {
           Info = material.SubPartCode,
           Description = material.Description,
           Qty = material.Qty
       }).ToList();
   

I suggest you go with the last option :)

One last comment - your if statement (materialUsed.Count > 0) is redundant because if collection is empty it won't go into the loop

Answer 2

You are referencing the same fixed index in your loop:

deliveryModel.Info = materialUsed[0].SubPartCode;

You need to use the loop variable:

deliveryModel.Info = material.SubPartCode;

Answer 3

You should use the current item in each iteration of the foreach loop instead of referencing the list. Try this:

IList<DeliveredTaskModel> deliveredTaskModel = new List<DeliveredTaskModel>();

        if (materialUsed.Count > 0)
        {
            foreach (var material in materialUsed)
            {
                var deliveryModel = new DeliveredTaskModel();
                deliveryModel.Info = material .SubPartCode;
                deliveryModel.Description = material .Description;
                deliveryModel.Qty = material .Qty;
                deliveredTaskModel.Add(deliveryModel);
            }
        }

Answer 4

IList<DeliveredTaskModel> deliveredTaskModel = new List<DeliveredTaskModel>();
// lines of code 

if (materialUsed.Count > 0)
{
    foreach (var material in materialUsed)
    {
        var deliveryModel = new DeliveredTaskModel();
        deliveryModel.Info = material.SubPartCode;
        deliveryModel.Description = material.Description;
        deliveryModel.Qty = material.Qty;
        deliveredTaskModel.Add(deliveryModel);
    }
}

materialUsed[0] is the first item of your list, and whetever the number of items the list has you take always the first, you should take the current item "material"