System.Collections.ObjectModel.Collection does not contain a definition for "Items"?

I’m following this article on how to build a Binary Tree in C# from msdn:

Microsoft Learn: Build skills that open doors in your career…(v=vs.80).aspx

But in Unity my code is producing the following error:

error CS0117: ‘System.Collections.ObjectModel.Collection >’ does not contain a definition for ‘Items’.

The offending code:

using System.Collections.ObjectModel; 

public class NodeList<T> : Collection<Node<T>>
{
    public NodeList() : base() { } 

    public NodeList(int initialSize)
    {
        for (int i = 0; i < initialSize; i++)
            base.Items.Add(default(Node<T>));
    }

    ....
}

Its the last line, which doesn’t recognize Items from the Collection class, even though it has Items: Collection<T> Class (System.Collections.ObjectModel) | Microsoft Learn

Also its not producing an error in visual studio… only the Unity editor. Is this a bug in the Unity editor or something of my own? Could someone try to reproduce this for me?

There is actually no current way to do what you are trying to do because unity only supports .net 3.5 and what you are trying to do requires 4.0 sorry :confused: