Author: Tomas Rutkauskas

I have a 3 level TTreeview. The nodes in levels 2 and 3 must have unique captions 
(text). Items will be added in a loop so I can't check the "Selected" text against 
the data to be entered. However, I will know which node where data entry will 
begin. If adding child nodes to a node on level 2 for example, I assume I need to 
loop through the children of the particular parent node of the node on level 2 and 
check the text property? Does this make sense?

Answer:

Yes. Use the edited nodes Parent.GetfirstChild to get a reference to the first 
child node of that parent. Then use that nodes GetNextSibling to find the next node 
on that level to examine, and so on. Untested:

1   function IsDuplicateNode(aNode: TTreenode): Boolean;
2   var
3     walker: TTreenode;
4   begin
5     Assert(Assigned(aNode), 'Need a node to examine!');
6     if Assigned(aNode.Parent) then
7       walker := aNode.Parent.GetFirstChild
8     else
9       walker := TTreeview(aNode.Treeview).Items[0];
10    Result := False;
11    while Assigned(walker) do
12    begin
13      if (walker <> aNode) and AnsiSametext(walker.Text, aNode.Text) then
14      begin
15        Result := true;
16        Break;
17      end;
18      walker := walker.GetNextSibling;
19    end;
20  end;