Question

In a C# Treeview, I need to remove all branches that do not contain values in a list in the leafs.
For example, I have a list { 112, 74 } and a Tree:
The Data Source is a self-joined table. So I can’t easily remove the unwanted leafs and branches.

Root
Branch1
Leaf 112
Leaf 1
Branch2
Leaf 74
Branch3
Leaf 44
Branch4
Leaf 99

I should end up with:
Root
Branch1
Leaf 112
Branch2
Leaf 74

Here is the code. It sort-of works. But the TrimTree only removes the bottom level. So I need to run this function a few times to completely remove all the empty branches. VERY inefficient.

    void GetTree(ref TreeView tv)
    {
     DataTable dt = c.GetTable("select id, parent_id, name from tbl_self_join_tree");
        tv.DataSource = new HierarchicalDataSet(dt, "ID", "Parent_ID");
        tv.DataBind();
    }

    void TrimTree(TreeNodeCollection nodes, List<string> l)
    {
        TreeNode node = null;
        for (int ndx = nodes.Count; ndx > 0; ndx--)
        {
            node = nodes[ndx - 1];
            if (node.ChildNodes.Count  == 0 && !l.Contains(node.Value))
                nodes.Remove(node);
            else   
                TrimTree(node.ChildNodes, l);
        }
    }

If I can write a better SELECT query, then I won’t need the TrimTree() function 😀
Solving this will help a LOT! Thank you so much!

Answer 1

It seems to me you can process parent nodes after processing child nodes. This way you can handle branches with all leafs deleted:

//DISCLAIMER: I didn't compile or test this method.
void TrimTree(TreeNodeCollection nodes, List<string> l)
{
    TreeNode node = null;
    for (int ndx = nodes.Count; ndx > 0; ndx--)
    {
        node = nodes[ndx - 1];
        TrimTree(node.ChildNodes, l);
        if (node.ChildNodes.Count  == 0 && !l.Contains(node.Value))
            nodes.Remove(node);
    }
}