How should I implement GetLastNode for TTreeNodes? - delphi

Question

When I need to find the first node in a TTreeView, I call TTreeNodes.GetFirstNode. However, I sometimes need to locate the last node in a tree and there is no corresponding TTreeNodes.GetLastNode function.
I don't want to use Items[Count-1] since that results in the entire tree being walked with Result := Result.GetNext. Naturally this only matters if the tree views have a lot of nodes. I fully appreciate the virtues of virtual container controls but I am not going to switch to Virtual TreeView just yet.
So far I have come up with the following:
function TTreeNodes.GetLastNode: TTreeNode;
var
Node: TTreeNode;
begin
Result := GetFirstNode;
if not Assigned(Result) then begin
exit;
end;
while True do begin
Node := Result.GetNextSibling;
if not Assigned(Node) then begin
Node := Result.GetFirstChild;
if not Assigned(Node) then begin
exit;
end;
end;
Result := Node;
end;
end;
Can anyone:
Find a flaw in my logic?
Suggest improvements?
Edit 1
I'm reluctant to keep my own cache of the nodes. I have been doing just that until recently but have discovered some hard to track very intermittent AVs which I believe must be due to my cache getting out of synch. Clearly one solution would be to get my cache synchronisation code to work correctly but I have an aversion to caches because of the hard to track bugs that arise when you get it wrong.

Answer 1

Although I am not a non-Exit purist, I think that when it is doable without Exit while keeping readability intact, one might prefer that option.
So here is exactly the same code, for I don't think you can get any other way (faster) to the end node, but without Exit and slightly more compact:
function TTreeNodes.GetLastNode: TTreeNode;
var
Node: TTreeNode;
begin
Node := GetFirstNode;
Result := Node;
if Result <> nil then
repeat
Result := Node;
if Node <> nil then
Node := Result.GetNextSibling;
if Node = nil then
Node := Result.GetFirstChild;
until Node = nil;
end;

Answer 2

The method I've used before is the maintain a TList using List.Add on the OnAddition event and List.Remove on the OnDeletion event (OnRemove?). You've access to List.Count-1 (or whatever you need) pretty much instantly then.
Post edit - I have to say that although this worked fine, I then grew up and moved to Virtual Tree View :-)

Answer 3

If I was to implement it, this would probably be my first draft.
function TTreeNodes.GetLastNode: TTreeNode;
var
Node: TTreeNode;
function GetLastSibling(aNode : TTreeNode) : TTreeNode;
begin
if not Assigned(aNode) then
EXIT(nil);
repeat
Result := aNode;
aNode := Result.GetNextSibling;
until not Assigned(aNode) ;
end;
begin
Node := GetFirstNode;
if not Assigned(Node) then begin
exit;
end;
repeat
Result := GetLastSibling(Node);
Node := Result.GetFirstChild;
until not Assigned(Node);
end;
I find this slightly more readable. It might be slightly slower though.
I'm unsure about whether or not this approach would be faster than items[Count-1], in some cases, it could be slower, as the TTreeNodes actually caches the last node accessed through the items property.