What design patterns do you apply in your practice?

In iOS development practice, the following design patterns are often used:

• MVC (Model-View-Controller) — separation of data, interface, and control logic.
• MVVM (Model-View-ViewModel) — separation of presentation from business logic using ViewModel, often with data binding.
• Singleton — for creating a single instance of a class, such as a settings manager or session.
• Delegate — for passing events between objects, widely used in UIKit.
• Observer (NotificationCenter, KVO) — for responding to state changes.
• Factory — for creating objects without specifying exact classes.

Example of using Delegate:

protocol DataReceiverDelegate: AnyObject {
    func didReceiveData(_ data: String)
}

class DataProvider {
    weak var delegate: DataReceiverDelegate?
    
    func fetchData() {
        // Fetch data
        let data = "Sample data"
        delegate?.didReceiveData(data)
    }
}

class ViewController: UIViewController, DataReceiverDelegate {
    let provider = DataProvider()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        provider.delegate = self
        provider.fetchData()
    }
    
    func didReceiveData(_ data: String) {
        print("Data received: \(data)")
    }
}