Accessing all the nodes in TreeView Control

Question

I have a TreeView Control with set of nodes and child nodes. For example:

ROOT has A,B,C.

A has a1, a2, a3 and then

Answer 1

I am not the biggest fan of recursion but it seems you must use it. I saw a clever example online mixing recursion with an iterator.

    private int GetLevels(TreeNodeCollection treeNodes)
    {
        int level = 0;
        foreach (TreeNode node in TreeTopDown(treeNodes))
        {
            int i = node.Level;
            if (i > level) level = i;
        }
        return level;
    }

    //TopDown Iterator 
    private IEnumerable TreeTopDown(TreeNodeCollection treeNodes)
    {
        foreach (TreeNode node in treeNodes)
        {
            yield return node;
            foreach (TreeNode subNode in TreeTopDown(node.Nodes)) yield return subNode;               
        }
    }

    //BottomUp Iterator
    private IEnumerable TreeBottomUp(TreeNodeCollection treeNodes)
    {
        foreach (TreeNode node in treeNodes)
        {
            foreach (TreeNode subNode in TreeBottomUp(node.Nodes)) yield return subNode;
            yield return node;
        }
    }