[Paraview] help: problem about message passing in paraview

[Nancy]

Hi, all,
     I am reading the source code of paraview, and want to understand the message passing scheme in paraview.
For example, when I push a button or choose an item in the menu on the client GUI, how this event is passed to the final related processing Class object?
I can only find the begin end of the source code (e.g. create a menu item) and the final class of processing (e.g. a reader/source class), but I can not track the message passing process between the begin end and final methods of related class.
    Who can give me an answer?   Thanks for any help!

Best,
Nancy