Answer.

Background

The Model-View-Controller (MVC) pattern is a classic architectural pattern that emerged long before Swift and is used to separate data, user interface, and control logic. In the history of iOS development, MVC was proclaimed by Apple as the main architectural pattern for building applications in Objective-C and Swift.

Problem

The main problem with standard MVC is that over time controllers become "Massive View Controllers", combining business logic, model interaction, user input handling, and even display logic. This leads to reduced readability, reusability, and testability of code.

Solution

In Swift, MVC is implemented using UIViewController classes for the controller, models as structs or classes, and UIView for building the interface. The controller connects the model and view, initiating interface updates when data changes.

Code example:

struct User {
    let name: String
    let age: Int
}

class UserView: UIView {
    let nameLabel = UILabel()
    func display(user: User) {
        nameLabel.text = "\(user.name), \(user.age) years old"
    }
}

class UserController: UIViewController {
    var user: User?
    var userView: UserView!

    override func loadView() {
        userView = UserView()
        view = userView
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        if let user = user {
            userView.display(user: user)
        }
    }
}

Key features:

Communication between layers through the controller.
The model is unaware of the view.
User input and navigation logic are in the controller.

Tricky Questions.

Is it acceptable to allow dependencies between View and Model directly in MVC?

No, the View should not interact with the Model directly. All communication occurs only through the Controller; otherwise, the model "learns" about the view, violating the principle of separation of concerns and hindering scalability.

Can the Controller contain business-level data and logic?

It is often mistakenly believed that the controller can contain business logic. In fact, business logic should be moved to the Model or separate services, while the controller should only manage the lifecycle of the View and data synchronization.

How to combat massive controllers (Massive View Controller)?

To combat massive controllers, move data processing out of the controller into the Model or services, use delegates, delegation patterns, and composition. Create separate classes for configuring the View or embed display logic directly into the View.

Common Mistakes and Anti-Patterns

The model communicates directly with the View
Massive controller (Massive View Controller)
State of the View stored in the controller
Lack of separation of business logic in the Model

Real-life Example

Negative case

In a project, the controller held both the user data and their processing, along with display code. Reusing logic in another controller turned out to be impossible, and testing business logic was very difficult.

Pros:

Quick start, few classes

Cons:

Poorly readable code
Difficulties with maintenance and testing

Positive case

The Model is responsible only for data and business logic, the View renders the interface, and the Controller connects them. This created the possibility to reuse components, test, and scale the application faster.