How does data exchange and interaction between system layers occur when creating a new application?

In iOS applications, interaction between layers is usually built according to architectural patterns (MVC, MVVM, VIPER, etc.).

Data exchange occurs through:

• Models: store data and business logic.
• Views: display data to the user.
• Controllers or ViewModels: manage logic and connect the model with the view.

Data is transmitted via methods, delegates, closures, or reactive libraries (e.g., Combine, RxSwift).

Example: The ViewModel receives data from the model and updates the View through binding or callback.

class ViewModel {
    var dataUpdated: (() -> Void)?
    private var data: [String] = [] {
        didSet {
            dataUpdated?()
        }
    }
    func fetchData() {
        // Get data from the model
        data = ["Item1", "Item2"]
    }
}

class ViewController: UIViewController {
    let viewModel = ViewModel()
    override func viewDidLoad() {
        super.viewDidLoad()
        viewModel.dataUpdated = { [weak self] in
            // Update UI
            self?.tableView.reloadData()
        }
        viewModel.fetchData()
    }
}