How do you implement the MVVM architectural pattern when developing with UIKit?

The architectural pattern MVVM (Model-View-ViewModel) in UIKit is implemented by dividing responsibilities among three components:

• Model — data and business logic.
• View — visual interface elements (UIView, UIViewController).
• ViewModel — an intermediary that transforms data from the model into a format suitable for display in the View.

Implementing MVVM in UIKit typically involves:

1. Creating a ViewModel that contains properties and methods for preparing data.
2. The ViewController subscribes to changes in the ViewModel (via KVO, Combine, RxSwift, or delegates) and updates the UI.
3. The ViewModel does not hold references to the View, which enhances testability.

An example of a simplified ViewModel:

class UserViewModel {
    var name: String
    var onNameChanged: (() -> Void)?

    private var user: User {
        didSet {
            name = user.name.uppercased()
            onNameChanged?()
        }
    }

    init(user: User) {
        self.user = user
        self.name = user.name.uppercased()
    }

    func updateName(_ newName: String) {
        user.name = newName
    }
}

In the ViewController, subscribe to onNameChanged and update the UI when data changes.