C# Object suddenly null

Question

I've searched so long and hard for this and now I'm at road's end. I've had this issue with more than this project, but I ended up scrapping the others. I have a code (C#) which is basically me trying to do Huffman tree. At one point I do this ("nodeList" is List(Node)):

Node node = new Node(nodeList[0], nodeList[1]);
nodeList.Add(node); // Adds a new node which includes two subnodes.

// Remove nodes from list (as they are now included in another node)
nodeList.RemoveAt(0);
nodeList.RemoveAt(1);

And the constructors in use here is:

// Constructor that takes nodes
public Node(Node left, Node right)
{
   leftNode = new Node(left);
   rightNode = new Node(right);
}

// Constructor that only takes 1 single node
public Node(Node copy)
{
   rightNode = copy.rightNode;
   leftNode = copy.leftNode;
   unencodedBits = copy.unencodedBits;
   encodingValue = copy.encodingValue;
   positions = copy.positions;
}

I did the second constructor as a hope that it would fix my problem (thinking that removing the node from the list maybe nulled it out.) (all of the values in my Node-class is on the right side of the second constructor.)

The problem: After doing the second "RemoveAt" the Node will no longer contain the two nodes. And I can not understand why. What do I have to do to prevent this from happening and why does it happen (so I can understand similar cases in the future)?

I probably forgot to include some vital information; If I did, please tell me. And thanks for any assistance.

Answer 1

Is your nodeList object in array or a List? If it is a list, then nodeList.RemoveAt(0) causes the node currently located and index 1 to now be located at index 0. so you would need to call

nodeList.RemoveAt(0); 
nodeList.RemoveAt(0); 

instead of

nodeList.RemoveAt(0); 
nodeList.RemoveAt(1);

see here: http://msdn.microsoft.com/en-us/library/5cw9x18z(v=vs.110).aspx