[flexcoders] Tree bug?

[Nick Durnell]

Hi all,

I have a tree containing lots of branches.  When a user opens a 
branch I add a load of leaf nodes to it.  I am running into problems 
where the new nodes are not displayed correctly.

Here is a sample application which demonstrates the problem:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"; width="200" 
height="300" layout="absolute" creationComplete="createTopNodes();">
  <mx:Script>
    <![CDATA[
      import mx.events.TreeEvent;
      import mx.collections.ArrayCollection;

      [Bindable] private var treeNodes:ArrayCollection = new 
ArrayCollection();

      private function createTopNodes():void
      {
        var newTestObj:TestObj;
        for (var i:int=1; i<=20; i++)
        {
          newTestObj = new TestObj();
          newTestObj.id = i.toString();
          newTestObj.children = new Array();
          treeNodes.addItem(newTestObj);
        }
      }

      private function itemOpenHandler(e:TreeEvent):void
      {
        var selectedObj:TestObj = TestObj(e.item);
        if (selectedObj.hasChildren)
        {
          return;
        }
        var newTestObj:TestObj;
        for (var i:int=1; i<=20; i++)
        {
          newTestObj = new TestObj();
          newTestObj.id = selectedObj.id + "_" + i.toString();
          newTestObj.children = new Array();
          selectedObj.children.push(newTestObj);
        }
        selectedObj.hasChildren = true;
      }
    ]]>
  </mx:Script>
  <mx:Tree id="testTree" width="100%" height="100%" 
dataProvider="{treeNodes}" labelField="id" itemOpen="itemOpenHandler
(event);"/>
</mx:Application>

This demo simply creates 20 top-level nodes and adds 20 child nodes 
whenever you open an existing node.

If you run the application and expand a node, the new child nodes are 
displayed down to the bottom of the visible tree area (all well and 
good).  However if you scroll down, the remaining sub-nodes are 
nowhere to be seen!  In fact, the visible sub-nodes have been drawn 
on top of the nodes at the top of the tree.  However if you close the 
node again and open it a second time everything is displayed as it 
should.

Is this a bug with the tree control or am I doing something 
completely wrong?  I need to create nodes like this on the fly as my 
tree is very big and I need to fetch child nodes from a database 
whenever the user opens a node in the tree.  I've tried adding calls 
to invalidateDisplayList and invalidateSize on the tree after 
creating the child nodes but this doesn't seem to make any difference.

Thanks,

Nick.