It's really strange when you need to look for good example on forums because you can't find it in official documentation .
Looks like you additionaly need to implement IExternalizable interface when your class needs to have parameters in constructor even if all fields of the class are public. At the same time you need to use default values for all parameters because: "Flash creates an instance of the object automatically before calling the object's readExternal() method".
You can find example here: http://forums.adobe.com/message/3085267#3085267
Shame on you Adobe, you must seriously improve quality of your documentation!
File a bug or comment on the livedocs page.