In my project I use the Model-View-Presenter and want to create a UI-Element where I can register a HandlerManager to handle client-side events.
How can I do something like this? Or does it not conform to MVP?
Well, if you are using the UiBinder paradigm, you can specify a UiHandler, using the @UiHandler annotation on your method (see here).
If you have more details on exactly what you're trying to do, then I can probably provide other solutions as well.