On Dec 2, 2008, at 5:48 PM, Mikael Wämundson wrote:
In my project I'm using instances of NSMutableArray containing
various objects. The arrays are used in the user interface through
NSArrayControllers with binding. In IB I'm thus accessing the
objects in the array through the controller.
In the code I have access to the array contents both through
instances of the controllers and instances of the arrays. In my
code, when do I use what? What is good programming? For example when
sorting the array contents, adding objects, changing values for
objects in the array…
Usually, the roles are arranged like this:
Model <-> Coordinating Controller <-> Mediating Controller (e.g.
NSArrayController) <-> View
If you're writing code for the model layer, of course it should just
directly operate on itself. If you're writing code for the
coordinating controller layer, it should interact with the model
directly, by going to its left in the diagram. It's pretty roundabout
and nonsensical for it to interact with the array controller, because
that will just have to turn around go back through the coordinating
controller in order to access the model.
If the coordinating controller isn't trying to modify the model, but
is trying to control the view, then it makes sense for it to sometimes
directly operate on the mediating controller. For example, sometimes
a sort operation is something you want to do to the model, to change
the actual ordering of elements in a to-many relationship within the
model. At other times, a sort operation is just for display. The
model doesn't need to change; just the way it's shown. In the latter
case, the coordinating controller would operate on the mediating
controller and perhaps the view.
How do you tell the difference? Well, remember that separating the
concerns is motivated by making the pieces reusable and independent.
A given model could be represented by different views (a table, a pie
chart, a web site, a command-line text-based listing, etc.). If the
operation is something which should be reflected no matter which view
or views are currently displaying the model, then it is an operation
on the model. If the operation is something which is just specific to
one particular view, then it should be handled by the mediating
controller and the view.
Cheers,
Ken
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