Graham Cox wrote:
On 30/11/2009, at 12:04 PM, Jason Stephenson wrote:
NSDocument and the document-based architecture in Cocoa is a bad
example of MVC.
As a statement that doesn't really stand up to scrutiny. Sure, you
can abuse NSDocument and violate MVC, but as it comes it does not. A
document might own (or be) the data model, and it might also keep a
list of window controllers. How does that violate MVC? NSDocument is
just 'M', and nothing more.
-makeWindowControllers and I disagree with you.
Let me rephrase what I said earlier:
NSDocument and the document-based architecture in Cocoa is a bad example
of MVC in as much as people confuse NSDocument with a document model
class when it is a model controller.--This is the confusion that I think
our friend Sandro is running into.
NSDocument doesn't merely represent the document's data as in a "pure"
MVC design, rather it is a controller for the document's data. The
subsection of the Document-Based Applications Overview entitled "The
Role of NSDocument" makes this abundantly clear. The actual model data
for the document is very often an ivar of the NSDocument subclass.
A data model should not be required to create controllers for GUI
elements as NSDocument is asked to do by NSDocumentController when a new
document is created. The creation and management of GUI elements is
typically a controller's job, not a model's job. A model should be
abstract in the sense that it is not tied to any particular visual
representation of the data. It should work in a command line application
as well as it works in a GUI application.--Admittedly, this is an ideal.
While NSDocument doesn't necessarily break MVC, I think the class is
poorly named. It should probably more properly be named
NSDocumentController and NSDocumentController would more properly be
named NSDocumentControllerController, but that's a bit awkward.
Now, I will stop before the moderators hit me with the moderation flag,
because I have a feeling we're going over old ground.
--Graham
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