From: Friedrich Dominicus <frido@...>
Date: 2002-09-17T14:32:45+09:00
Subject: Re: MVC and OO Design?

jcb@iteris.com (MetalOne) writes:

> Thanks to all for your help.
> 
> I was really thinking very abstractly about a problem in my head that
> MVC kind of demonstrated.  I was in search of deep answers in regards
> to when to include a function in a class and when not too.  The common
> wisdom states that when a function needs access to the classes data,
> it should be included with the class.  MVC strays from this notion
> because the View needs access to the Models data and yet the View
> functions are not placed in the class. 
That is not true. the view does know nothing about the Model the only
one which knows of it is the Controller. But you have to provide all
the access functions a Controller may need in both the View and the
Model. I'll try to show a simple example (not Ruby) 


Modell
   a number a 
   a number b

   model work is 
        add a b


View
   a textfield a_number
   a textfield b_number
   a output field c_number

   accessors to a_number b_number
   setter for c_number


Controller
    Model class
    View class

    Controller get data from View
        query the content of the view
        my_a = View.get_textfield_a_content
        my_b = View.get_textfield_b_content
    ask the model do it's work out the work
    my_sum = Model.add(a, b);
    
    update the view
    View.set_c_number(my_sum)


.....

You can write that example down nearly one-to-one in Ruby. You just
have to to know the Ruby GUI classes. But you see it fit's perfectly
into the OO model. Controller does not know about the inners of both
it just uses the official available interface provided by Model, but
the view and the Model do not know anything from each other. All this
knowledge is bundeled in the Controller. 

I hope this clarifies it.
Regards
Friedrich