C# Editing items of two lists with same references

Question

I have a List of myClass objects (some elements are added before)

List<myClass> myClassList1;

Then I copy some of the elements in this list into another list

List<myClass> myClassList2 = new List<myClass>();
foreach (myClass obj in myClassList1)
{
  myClassList2.Add(obj);
}

This list is now sorted

myClassList2.sort();

And then I want to modify the first element in this sorted list

myClassList2[0].id++;

Problem: in the myClassList2 this element is modified, but not in myClassList1 .

I thought adding myClass objects to a list will add a reference to this object, so i can modify it in the list (this was the actual plan).

Answer 1

It does update myClassList1 as you expect. You might want to post your code. Here's my code that updates both lists.

    public class myClass
    {
        int _id;
        public myClass(int id)
        {
            Id = id;
        }
        public int Id
        {
            get
            {
                return _id;
            }
            set
            {
                _id = value;
            }
        }
    }

    public void BuildList()
    {
        List<myClass> myClassList1 = new List<myClass>();
        myClassList1.Add(new myClass(8));
        myClassList1.Add(new myClass(4));
        myClassList1.Add(new myClass(10));
        myClassList1.Add(new myClass(1));   // This would become the first item when the list is sorted.
        myClassList1.Add(new myClass(30));

        List<myClass> myClassList2 = new List<myClass>();
        foreach (myClass obj in myClassList1)
        {
            myClassList2.Add(obj);
        }

        myClassList2.Sort((s1, s2) => s1.Id.CompareTo(s2.Id));  // Sort by Id.

        // Modify the first element in the second sorted list.
        myClass firstElementList2 = myClassList2[0];
        firstElementList2.Id++;
        int valueInList2 = firstElementList2.Id; // Get the id that is incremented

        // Find the same object in first list...
        myClass sameElementInList1 = myClassList1.Find(x => x.Id.Equals(valueInList2));
        int valueInList1 = sameElementInList1.Id;

        if (valueInList2== valueInList1)
        {
            MessageBox.Show("Cheers!");
        }
    }

To test:

[TestMethod]
        public void SKTestMethod()
        {
            Class1 c1 = new Class1();
            c1.BuildList();
        }