Flex: Updating data provider of mx:tree

I create a mx:tree with flex and its data provider is an array collection. In addition, this array collection is set by using a database. This process is handled with an event listener function. Database returns data to array collection asynchronously. And this is the problem that when flex application is started array collection is not fully initialized. Hence, mx:tree is incomplete. Here is the code segment:

protected function populateTreeNode(node:Object):void
        {

            if (node != null && node["className"] != "InventoryCategory") return;

            var categoryId:Number = 0;
            if (node != null)
                categoryId = node["id"];

            DAOUtil.loadAll("InventoryCategory", EventUtil.handleWithArgs(popoluateTreeNodeHandler, [node, "InventoryCategory"]), "categoryId", categoryId.toString());
            DAOUtil.loadAll("InventoryItem", EventUtil.handleWithArgs(popoluateTreeNodeHandler, [node, "InventoryItem"]), "categoryId", categoryId.toString());
        }

        protected function popoluateTreeNodeHandler( event : Event , nodeCategory:Object, typeName:String): void
        {
            var items:Array = DAOUtil.getArray(event, typeName);
            items = LangUtil.fromNameField(items);

            if (nodeCategory != null)
                nodeCategory["children"] = items;
            else
                inventoryArray.addAll(new ArrayCollection(items));


            for each (var item:Object in items) populateTreeNode(item);

        }

This function tries to initialize array collection recursively and at the end of the populateTreeNodeHandler function it is fully initialized. But when flex application is started, it is sometim开发者_StackOverflow中文版es incomplete. Is there any solution to this problem?

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Problem is fixed. Problem is the fulfilling the data provider array two times. One of them fulfill the array with category items correctly but the other one empty the data provider array.