CODEWITHSUNDEEP
swiftmodel-view-controllermvvmarchitecture
Timo Ernst
Timo Ernst

Reputation: 15973

Are MVVM-based applications required to have a controller?

I'm having a hard time wrapping my head around MVVM as I'm in the progress of learning SwiftUI development with Swift for iOS. After reading various tutorials and watching YouTube videos, this is my understanding:

However, after doing additional research, I found this article which talks about the role of controllers in MVVM. Now, this confuses me a lot because my understanding was that the ViewModel in MVVM already takes care of what a controller would do e.g. in MVC and therefore controllers would not exist in apps based on MVVM.

Question: Do controllers exist in apps based on MVVM or is the article simply wrong?

Upvotes: 1

Views: 699

Answers (1)

Rob
Rob

Reputation: 437402

It is merely a question of terminology. This author’s choice of terminology is a bit unusual, and I would not get hung up on that. As you dive into these architectural patterns, you’re going to see all sorts of different uses of terminology. (Usually it is the term “view model” that is subject to some creative interpretation.)

Regarding this author’s particular use of the term “controller”, earlier in the document, when talking about view controllers, he starts referring to them as simply “controllers”. This is imprecise, but it is the terminology that he adopts throughout the article.

(As an aside, I would avoid referring to view controllers just as “controllers”, because for many of us, the term “controller” refers to something far more abstract, unrelated to the UI. E.g., see the discussion of “controllers” late in Dave Delong’s excellent video A Better MVC. But let’s set all of that aside and talk about the role of view controllers in MVVM.)

If you are employing MVVM in UIKit or AppKit, then you have a model, a view, and a view model. But you still have view controllers, too. So what happens to them? They do not disappear (unless you switch to something like SwiftUI).

Most/many of us simply consider the view controller as part of the broader “view” layer. A view controller is a UIKit object. It configures views. It is not some abstract object, but rather is an integral part of the UI. In MVVM, it often bears responsibility for hooking up the views to the view model, etc. Regardless of what architectural pattern you adopt, the hallmark of a good view controller implementation is that it is almost entirely restricted to UI related tasks.

So, in short, in that article you reference, the author is merely saying that view controllers are still in the mix (for non-SwiftUI projects, at least). He decided to describe it as a separate layer in his MVVM diagram. Many of us just consider the view controllers to just be part of the “view” layer. It is a question of terminology.

Upvotes: 7

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