Why I cannot inherit LinkedListNode<T>?

Question

In .NET 3.5, I am using the LinkedList class but I am having the following issue. I want the items of that list to be aware of the previous and next items in the list. In other words, I want the method in the items to be able to do this.Next, this.Previous. Is this possible? Below is an example of what I would like to do.

Day d1 = new Day();
Day d2 = new Day();
LinkedList<Day> days = new LinkedList<Day>();
days.AddLast(d1);
days.AddLast(d2);

// Here is want I would like to do
d1.Next = ...

Thanks!

Answer 1

First, LinkedListNode is sealed so it can not be inherited.

Secondly, LinkedListNode does contain properties Previous and Next that refer to the previous and next nodes in the LinkedList that a given instance of LinkedListNode came from.

Lastly, to use AddLast correctly, you must do the following:

Day d1 = new Day();
Day d2 = new Day();
LinkedList<Day> days = new LinkedList<Day>();
LinkedListNode<Day> node1 = days.AddLast(d1);
LinkedListNode<Day> node2 = days.AddLast(d2);

// now node1.Next refers to node containing d2
// and node2.Previous referes to node containing d1

Answer 2

You're using it wrong.

The .AddLast(T) method returns a linked list node. This points to your day and has the prev and next functions you are looking for.

Answer 3

According to the MSDN, the LinkedListNode class cannot be inherited.

Michael points out that this blog post from Eric Lippert talks about why many classes in the framework are sealed