Indicate children in a virtual string tree without actually loading them

>   Node.States := Node.States + [vsHasChildren];

That's the wrong way to do it!
That way only the node knows, the tree itself doesn't so the tree isn't updated.
use:

VirtualStringTree.HasChildren[Node] := true;

Excellent, thanks Steve.

Interestingly the treeview doesnt seem to be very responsive to change in states visually.

Either if I use
VirtualStringTree.HasChildren[Node] := true;
or
Node.States := Node.States + [vsHasChildren];

The + sign doesn't seem to disappear unless you actually try and click it.
Is there a repaint issue?

I am doing the Node.States := Node.States + [vsHasChildren]; in the InitNode event and it has always work for me. At the time I do this there are, in fact, no childern for that node and I determine if there are children in OnExpanded event.

So you are setting all your nodes to be marked as having children and then when you click to expand the node, it removes the + if it cannot find any?

That is exaclty what I am doing. Becuase my data are dynamic - in order for that work properly I also have to delete the children when the node is colapsed.

> I am doing the Node.States := Node.States + [vsHasChildren]; _in the InitNode event_

ah, you didn't mention that, afaik this will only work in the initnode event, not somewhere else

I'm pretty much doing something similar to you Steve but I'm not deleting the children when collapsing.

procedure TfmTreeViewTest.VirtualStringTree1Expanding( sender: TBaseVirtualTree;
   Node: PVirtualNode; var Allowed: Boolean);

var
   curObject: TObject;
begin
   inherited;
   // checks if children have already been populated and if so allows the node
   // to expand without trying to add the children again
   if sender.childCount[ node] > 0 then
   begin
      allowed := true;
      exit;
   end;

   if assigned( node) then
   begin
      curObject := TObject( sender.getNodeData( node)^);
      allowed := buildChildNodes( node, curObject);
   end;
end;

Anyway, thanks for the information both of you.

see also this: http://support.soft-gems.net/forums/viewtopic.php?t=781&highlight=isvisible

it's on node visibility, but same applies to HasChildren.

note the bold part written by the author of TVirtualTree :)

Interesting. I have changed my code to vTree.HasChildren[Node] := True; and this work just as well.
I cannot think of a good reason to contradict MerijnB nor would I wish to question the authority of Mike Lischke (he's written a true awesome component). Thanks for setting me straight MerijnB.
This reminds me why I participate here  I frequently learn more when answer Qs than when asking them.
Sorry about the points ;-)

I don't care about the points, sharing knowledge (me to others as well as others to me) is much more fun.
The thing is that if you change something in a node record, the tree doesn't know it, so it won't update until it 'accidentally' comes across that changed value for that node. It does work in OnInitNode because the tree will check the node right after that.

Yeah sorry about the points, I would have shared them between the two of you if I wasn't so quick to accept :o)