In MVC where do you put references to your model Classes?

Question

I have been wondering for a while, after asking different people and without any of them providing what I would call an "at least a bit concrete answer":

Question:

Where, in an iPhone application should an application keep the references to it's Model Classes (using the MVC approach) ?

In iPhone (and Cocoa) applications we have what we call the "App Delegate", which basically start's up our application and inits our controllers, also handles UITouch events.

So is the App Delegate a controller ? a model class ? none of the two ? I think not knowing that also makes confusing to know where to put the Model References.

Example:

You have the Application Delegate, that delegate contains a reference to your Application's View Controller. If my Application would use Model Class A ( which is a webserver daemon class ), and a Class B which stores data queried by that webserver.

Where would you guys store the references to A and B ? (App Delegate ? View Controller ? Both ? )

There are many options here, but as an example, I would really like to know how would you guys use mvc to put together this application which only uses one View.

Answer 1

It is tempting to put everything in the AppDelegate, but if you start doing this, then your AppDelegate will be full of reference hacks. If you are doing a strict MVC, then you should have 3 things:

• A Model
• A View Controller (Only for view logic)
• A Controller (For coordinating between the view and the model)

So for example, I have a model Foo and a Foo controller. I would have:

• Foo.m (Model)
• FooViewController.m (Displays a Foo)
• FooController.m (Controls the logic)

And finally, to answer your question, I would store my references to Foo's in the foo Controller. I like to use singletons for my controllers, but thats just me. If you do use a singleton, you can just do something like this: [[FooController sharedInstance] listOfFoos] to get your Foo's

Answer 2

In my applications I usually rename the AppDelegate class to AppController, if that helps explain things better conceptually. Your app controller is responsible for creating and/or configuring the model controller (which manages your collection of model objects) and window or view controllers, setting up references between them if needed, and calling methods on these controllers in response to NSApplication delegate methods or high level action methods from the main menu. Depending on how complex your application is you might also have additional model or view controllers which are created outside your app controller.

Of course if you have a simple application there's no real reason not to have your app controller play the role of the model controller if you want. What you want to avoid is file with hundreds of lines of code, all doing conceptually unrelated tasks.