JavaFX 2.0 :: TreeItem And Custom Rendering

I am fairly new to FX but well experienced with Swing. Since I am familiar with the Swing concept of rendering a let's say JTree I got problems with the FX model of - in this case - TreeView.
 
I read several documentations about FX. From the API doc of TreeItem I adapted the file browser example to create an own class like this :
 
public class PathTreeItem extends TreeItem<PathTreeItem> implements
        Comparable<PathTreeItem> {
    private boolean firstVisit = true;
    private boolean readable;
    private boolean dir;
    private boolean symlink;

[Code] ...
 
But this did not change anything. I try to override toString() in both classes but even this did not change anything.
 
What I wonder so far:
 
Why is item in PathNodeTreeCell always null?What is the difference between the item I get in the updateItem method and the one I get from getItem() (line 10)How can I connect the PathTreeItem class to the PathNodeTreeCell classShould I always call super() in the constructors? (I delved a little bit in the sources of TreeItem and TreeCell and I found some setup code there )Is it ok to extend TreeItem in the way I does for my custom PathTreeItem class? ( I wonder if this is a cyclic dependency when I extends TreeItem in this way )How can I sort the nodes? I added the Comparable interface but this not change the sorting of the nodesAre ther some tutorials of TreeItem/TreeCell with no trivial objects like String ? 

I want to adapt an well running Swing application to FX. In the Swing app I used a mechanism to load the child path's of a directory in a separate thread to avoid freezing if the UI if there are much child elements. I guess in FX I should use the Properties pattern to achieve this should I?