Discuss on MVC implementation on iPhone

Question

Im a using the MVC pattern for a while on different frameworks such as (swing, android, gwt ...) Now, I\'m learning the iPhone framework and I am quite surprised about MVC imple

Answer 1

MVC has meant different things since it was first formalized in Smalltalk, and the NeXTSTEP (Cocoa) version of MVC doesn't exactly match up with Smalltalk's. Smalltalk's break-down is basically like this:

• The Model holds data
• The View presents data
• The Controller manages user interaction

NeXTSTEP's break-down is in practice more like this:

• The Model holds the data
• The View draws the data
• The Controller manages the "logic" (including the "presentation" portion of drawing data)

I'm differentiating here between drawing and presenting in that NSView tends to be dumb about the "meaning" of the data. It just focuses on drawing pixels. So you tend to pass it actual strings rather than an object that the view tears apart and "presents."

It's not a huge difference, but it is the cause of things like what you're running into. The main shift IMO, is that with Cocoa/NeXTSTEP, the view classes have become more and more reusable. In becoming so reusable, more of the application-sensitive portions have needed to move out into the controller. This I believe is generally a benefit because it leads to fewer subclassses, more understandable code and more reusable code... most of the time. In particular, it allows you to more easily swap in views that do fancier drawing (a view that animates a particular way or alternates colors on rows or the like) without bumping into any application-specific logic which generally lives in the controllers.

That said, when a view is particularly complex, I do find it beneficial to create more specialized views that take a data object and manage their own presentation, more in the way I believe you are envisioning.

EDIT: One additional thing to note. Apple's example code often is terrible in terms of design. They almost never include model classes at all, and cram almost everything imaginable into the ViewControllers and worse: the AppController (which should be a very simple object in my opinion). This is generally because their sample code is trying to demonstrate some specific point and they don't want to include the complexity of breaking things up (or the author is being lazy; take your pick). So while I do believe that smart view controllers often work out well, you shouldn't take the example code as a demonstration of this. Unfortunately, there aren't a lot of canonical examples out there of good application-level Cocoa design, since most Cocoa apps are closed source. One good example to learn from is Adium. It is an excellent example of a large, well-designed, multi-developer Cocoa app.