Updating Custom Class in List<T>

Question

I am trying to update a List which is a List of Interfaces to concrete classes.

I add to the List each Market type i am interested in, for this Example these Markets are A and B

I loop over all the markets, (sample provided with 3 markets A B & C, we are only interested in A and B) And determine which is of interest to us.

Once found we pass this to an extraction method too do its work and create an instance of the Correct Market_ class type.

This all works fine, but when i try to update the list with the Updates it does not get reflected in the List.

Code below, any Suggestions?

Thanks

public class Test
{
    public Test()
    {
        TheMarkets MarketsToUpdate = new TheMarkets();
        List<SpecificCompanyMarket> lstMarks = new List<SpecificCompanyMarket>();

        lstMarks.Add(new SpecificCompanyMarket(1234, "A", "Some HTML DATA HERE"));
        lstMarks.Add(new SpecificCompanyMarket(5874, "B", "Some HTML DATA HERE"));
        lstMarks.Add(new SpecificCompanyMarket(2224, "C", "Some HTML DATA HERE"));

        foreach (var item in lstMarks)
        {
            if (MarketsToUpdate.IsMarketWeAreInterestedIn(item.MarketName))
            {
                ITheMarkets MarkToUpdate = ExtractMarketData(item);

                var obj = MarketsToUpdate.MarketsWeAreInterestedIn.FirstOrDefault(x => x.MarketName() == "A");

                if (obj != null)
                {
                    obj = MarkToUpdate;
                }

            }
        }

        //Look At MarketsToUpdate Now and the item has not changed, still original values

        //I was expecting to see the new values for the fields in A, not the default 0's
    }

    public ITheMarkets ExtractMarketData(SpecificCompanyMarket item)
    {
        ITheMarkets market = null;

        if (item.MarketName.ToUpper() == "A")
        {
            Market_A marketType = new Market_A();
            marketType.SomeValue1 = 123;
            marketType.SomeValue2 = 158253;

            market = marketType;
        }
        //Other Market extractions here

        return market;
    }


}

public class SpecificCompanyMarket
{
    public int MarketId { get; set; }
    public string MarketName { get; set; }
    public string MarketDataHTML { get; set; }

    public SpecificCompanyMarket(int MID, string MName, string MData)
    {
        MarketId = MID;
        MarketName = MName;
        MarketDataHTML = MData;
    }
}

public class TheMarkets 
{
    public List<ITheMarkets> MarketsWeAreInterestedIn = new List<ITheMarkets>();

    public TheMarkets()
    {
        Market_A A = new Market_A();
        Market_B B = new Market_B();

        MarketsWeAreInterestedIn.Add(A);
        MarketsWeAreInterestedIn.Add(B);
    }

    public bool IsMarketWeAreInterestedIn(string strMarketName)
    {
        bool blnRetVal = false;

        foreach (var item in MarketsWeAreInterestedIn)
        {
            if (item.MarketName().ToUpper().Trim().Equals(strMarketName.ToUpper().Trim()))
            {
                blnRetVal = true;
                break;
            }
        }

        return blnRetVal;
    }
}

public interface ITheMarkets
{
    string MarketName();
}

public class Market_A : ITheMarkets
{
    public string LabelType { get; private set; }

    public double SomeValue1 { get; set; }
    public double SomeValue2 { get; set; }
    public double SomeValue3 { get; set; }

    public Market_A()
    {
        LabelType = "A";
    }

    public string MarketName()
    {
        return LabelType;
    }
}

public class Market_B : ITheMarkets
{
    public string LabelType { get; private set; }

    public List<string> SomeList { get; set; }
    public double SomeValue { get; set; }

    public Market_B()
    {
        LabelType = "B";
    }

    public string MarketName()
    {
        return LabelType;
    }
}

Answer 1

You are not storing "list of interfaces" in your list. List<T> stores an array of pointers to objects that support T interface. Once you enumerate (with Linq in your case) your list, you copy a pointer from list, which is not associated with list itself in any way. It is just a pointer to your instance.

To do what you want, you will have to build new list while enumerating the original one, adding objects to it, according to your needs, so the second list will be based on the first one but with changes applied that you need.

You can also replace specific instance at specific index instead of building new list in your code, but to do this you will need to enumerate your list with for loop and know an index for each item:

list[index] = newvalue;

But there is a third solution to update list item directly by Proxying them. This is an example

class ItemProxy : T { public T Value { get; set; } }

var list = new List<ItemProxy<MyClass>>();
list.Insert(new ItemProxy { Value = new MyClass() });
list.Insert(new ItemProxy { Value = new MyClass() });
list.Insert(new ItemProxy { Value = new MyClass() });

foreach(var item in list)
if(item // ...)
item.Value = new MyClass(); // done, pointer in the list is updated.

Third is the best case for perfomance, but it will be better to use this proxying class for something more than just proxying.

Answer 2

This is a short example to get you going. Loop through your list, find the object you want to update, create a new object of that type and then find the original objects index in the list and overwrite it in place. You are essentially just replacing the object in the list with a new one not mutating the existing one.

foreach (var item in lstMarks)
{
    //your code to get an object with data to update    
    var yourObjectToUpdate = item.GetTheOneYouWant();

    //make updates
    yourObjectToUpdate.SomeProperty = "New Value";

    int index = lstMarks.IndexOf(item);
    lstMarks[index] = yourObjectToUpdate;
}

Answer 3

You are extracting an obj from marketWeAreInterestedIn list using LINQ's firstOrDefault extension. This is a new object and not a reference to the obj in that list. Therefore, no updates will be reflected in the object inside that list. Try using 'indexof'