[Arp] Central dispatcher

[Nils Millahn]

Hi All,

(just realised I kept calling it event dispatcher rather than central 
dispatcher ;) just ignore please ;))

I've been thinking about this for a while and have used similar 
techniques in my own projects but I don't think it's the right approach 
- it makes life easier but doesn't reduce dependencies amongst the 
forms/views.

First off - if you want to use a central dispatcher, I think there is 
already a perfect place for it - the main Application form, which 
contains all views. That could inherit from EventDispatcher or perhaps 
implement an EventDispatcher interface, to relay events from and to its 
child forms.

The reason I don't think it reduces dependencies is that you will still 
write code in a child form that specifically reacts to an event 
broadcast by another. Eg - Form A broadcasts event, Form B receives that 
event (via EventDispatcher) and handles it - so there is a method in 
Form B that interacts with Form A on a very basic level.

The question for me is always - if you removed Form A from the 
application, would there be code left in Form B that was made redundant 
- and the answer is clearly 'yes'. Similarly, if you didn't have access 
to a child form's class code, could you still make it react to the event 
- and the answer would be 'no'.

But I think that the ARP structure already addresses these issues - the 
main Application form is the right place to handle these events. It is 
the only place that should have specific knowledge about the other forms 
- after all, they are its children. You give each child Form the 
functionality it requires - but don't give it the means to react to 
other child forms' events. The main Application form however does listen 
to events from its child forms and then calls specific methods in each 
child to react to that event.

Benefits:
- all code that reacts to a specific event is contained in a single 
method - if you don't want to react to that event anymore, you don't 
need to edit each child form's class
- the child forms remain self-contained - no code dependencies (you 
develop functionality to do what you need it to but don't include the 
code to react to the events)

etc :)

- Nils.