Protocol-oriented architecture in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Protocol Extensions

What will be printed when the following Swift code runs?

iOS Swift

protocol Greetable {
  func greet() -> String
}

extension Greetable {
  func greet() -> String {
    return "Hello from protocol extension"
  }
}

struct Person: Greetable {}

let p = Person()
print(p.greet())

A Hello from protocol extension

B Error: Protocol method not implemented

C Hello from Person struct

D Runtime crash

💡 Hint

Protocol extensions provide default implementations.

Since Person does not implement greet(), the default implementation from the protocol extension is used.

❓ ui_behavior

intermediate

Protocol and UIViewController Behavior

Given a protocol with a default method to setup UI, which option correctly applies the protocol to a UIViewController subclass and calls the setup method?

iOS Swift

protocol UISetup {
  func setupUI()
}

extension UISetup {
  func setupUI() {
    print("Default UI setup")
  }
}

class MyViewController: UIViewController, UISetup {
  override func viewDidLoad() {
    super.viewDidLoad()
    // Call setupUI here
  }
}

A override func viewDidLoad() { super.viewDidLoad(); self.setupUI }

B override func viewDidLoad() { super.viewDidLoad(); self.UISetup.setupUI() }

C override func viewDidLoad() { super.viewDidLoad(); setupUI() }

D override func viewDidLoad() { super.viewDidLoad(); UISetup.setupUI() }

💡 Hint

Call the protocol method directly on self.

The protocol method setupUI() is available on self because MyViewController conforms to UISetup. Calling setupUI() inside viewDidLoad works.

❓ lifecycle

advanced

Protocol-oriented Initialization

What error occurs when trying to compile this Swift code?

iOS Swift

protocol Identifiable {
  var id: String { get }
  init(id: String)
}

struct User: Identifiable {
  let id: String
  init(id: String) {
    self.id = id
  }
}

let user = User(id: "123")

A Error: Type 'User' does not conform to protocol 'Identifiable' because init(id:) is missing

B No error, compiles and runs fine

C Error: Cannot use init in protocol

D Runtime error: Missing initializer

💡 Hint

Structs do not inherit protocol initializers automatically.

User must implement the required init(id:) initializer explicitly to conform to Identifiable.

❓ navigation

advanced

Protocol and Navigation Controller

Which option correctly uses a protocol to define a navigation action and implements it in a UIViewController subclass?

iOS Swift

protocol Navigatable {
  func navigateToDetail()
}

class ListViewController: UIViewController, Navigatable {
  func navigateToDetail() {
    let detailVC = UIViewController()
    // Navigate to detailVC
  }
}

A navigationController?.pushViewController(detailVC, animated: true)

B self.show(detailVC)

C present(detailVC, animated: true)

D detailVC.navigationController?.pushViewController(self, animated: true)

💡 Hint

Use navigationController to push new view controller.

To navigate in a navigation stack, pushViewController is used on navigationController.

📝 Syntax

expert

Protocol Composition and Method Resolution

What is the output of this Swift code?

iOS Swift

protocol A {
  func foo() -> String
}

protocol B {
  func foo() -> String
}

extension A {
  func foo() -> String { "From A" }
}

extension B {
  func foo() -> String { "From B" }
}

struct C: A, B {}

let c = C()
print(c.foo())

A From A

B From B

C Runtime crash

D Error: Ambiguous use of 'foo()'

💡 Hint

Multiple protocol extensions provide the same method.

The compiler cannot decide which foo() to use because both A and B provide default implementations, causing ambiguity.