Returns nodes which are on screen (Expanded) as ObjectArray.
This does not only return nodes that are currently on the screen but all nodes that are within expanded scope. For example a node which is a child of a Collapsed node will not be returned.
This array is the same correct linear order as the nodes appear on the screen.
Warning
Do not use the ObjectArray returned by this function for anything else than to read from it. Inserting or deleting from the ObjectArray can and will cause unexpected results in the TreeView.