Protocols in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a protocol named Drivable.

iOS Swift

protocol [1] {
  func drive()
}

Drag options to blanks, or click blank then click option'

ADrivable

BDriveable

CDriving

DDrive

Attempts:

3 left

💡 Hint

Common Mistakes

Misspelling the protocol name.

Using a verb form instead of an adjective.

The protocol name should be Drivable to match the task requirement.

2fill in blank

medium

Complete the code to make the class Car conform to the Drivable protocol.

iOS Swift

class Car: [1] {
  func drive() {
    print("Driving the car")
  }
}

Drag options to blanks, or click blank then click option'

AVehicle

BDrivable

CDriveable

DRunnable

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong protocol name.

Forgetting to conform to the protocol.

The class must conform to the Drivable protocol to implement its requirements.

3fill in blank

hard

Fix the error in the protocol method declaration to make it optional.

iOS Swift

@objc protocol Drivable {
  [1] func drive()
}

Drag options to blanks, or click blank then click option'

Aoptional

B@optional

C@objc optional

Doptional func

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'optional' keyword alone.

Missing the @objc attribute on the protocol.

In Swift, to make a protocol method optional, the protocol must be marked @objc and the method marked @objc optional.

4fill in blank

hard

Fill both blanks to declare a protocol Playable with a property and a method requirement.

iOS Swift

protocol Playable {
  var isPlaying: [1] { get set }
  func [2]()
}

Drag options to blanks, or click blank then click option'

ABool

Bplay

CInt

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property type.

Using incorrect method name.

The property 'isPlaying' should be of type Bool, and the method name should be 'play' to match the protocol requirements.

5fill in blank

hard

Fill all three blanks to implement the Playable protocol in class MusicPlayer.

iOS Swift

class MusicPlayer: Playable {
  var isPlaying: [1] = false
  func [2]() {
    isPlaying = true
    print("Music started")
  }
  func [3]() {
    isPlaying = false
    print("Music stopped")
  }
}

Drag options to blanks, or click blank then click option'

ABool

Bplay

Cstop

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property type.

Incorrect method names like 'start' instead of 'play'.

The property 'isPlaying' is Bool. The 'play' method fulfills the protocol requirement, and 'stop' is an additional method.

Practice

1. What is the main purpose of a protocol in Swift?

easy

A. To create a new class with default behavior

B. To define a blueprint of methods and properties that a type must implement

C. To store data persistently on the device

D. To handle user interface layout automatically

Solution

1. Step 1: Understand what a protocol defines

   A protocol specifies methods and properties that a type must implement, acting as a blueprint.

2. Step 2: Differentiate from other concepts

   Protocols do not create classes or store data; they only define requirements.

3. Final Answer:

   To define a blueprint of methods and properties that a type must implement -> Option B

4. Quick Check:

   Protocol purpose = blueprint [OK]

Hint: Protocols define required methods and properties [OK]

Common Mistakes:

• Confusing protocols with classes
• Thinking protocols store data
• Assuming protocols handle UI layout

2. Which of the following is the correct syntax to declare a protocol named Drivable in Swift?

easy

A. struct Drivable { func drive() }

B. class Drivable { func drive() }

C. func protocol Drivable() { drive() }

D. protocol Drivable { func drive() }

Solution

1. Step 1: Identify correct protocol declaration syntax

   Protocols are declared with the keyword protocol followed by the name and curly braces.

2. Step 2: Check method declaration inside protocol

   Methods inside protocols are declared without implementation, just the signature.

3. Final Answer:

   protocol Drivable { func drive() } -> Option D

4. Quick Check:

   Protocol syntax = keyword 'protocol' + name + method signatures [OK]

Hint: Use 'protocol' keyword, not class or struct [OK]

Common Mistakes:

• Using class or struct instead of protocol
• Adding method implementation inside protocol
• Incorrect keyword order

3. Consider this Swift code:

protocol Greetable {
  func greet() -> String
}

struct Person: Greetable {
  func greet() -> String {
    return "Hello!"
  }
}

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

What will be printed when this code runs?

medium

A. Hello!

B. greet()

C. Error: Missing protocol implementation

D. nil

Solution

1. Step 1: Check protocol and struct conformance

   The struct Person adopts Greetable and implements the required greet() method returning "Hello!".

2. Step 2: Understand the print statement output

   Calling p.greet() returns "Hello!", which is printed.

3. Final Answer:

   Hello! -> Option A

4. Quick Check:

   Implemented method returns "Hello!" [OK]

Hint: Implemented protocol methods run normally [OK]

Common Mistakes:

• Expecting protocol name printed
• Thinking missing implementation error occurs
• Assuming nil is printed

4. What is wrong with this Swift code?

protocol Runnable {
  func run()
}

struct Athlete: Runnable {
  // Missing run() implementation
}

medium

A. No error, code is valid

B. Error: run() must have a return type

C. Error: Athlete does not implement required method run()

D. Error: Protocol Runnable cannot be adopted by struct

Solution

1. Step 1: Check protocol requirements

   The protocol Runnable requires a method run() with no return value.

2. Step 2: Verify struct conformance

   The struct Athlete adopts Runnable but does not implement run(), causing a compile error.

3. Final Answer:

   Error: Athlete does not implement required method run() -> Option C

4. Quick Check:

   Missing required method causes error [OK]

Hint: All protocol methods must be implemented [OK]

Common Mistakes:

• Assuming structs can't adopt protocols
• Thinking missing method is allowed
• Expecting run() to require return type

5. You want to create a protocol Vehicle with a property speed that can be read and set. Which of these protocol declarations is correct?

hard

A. protocol Vehicle { var speed: Int { get set } }

B. protocol Vehicle { var speed: Int }

C. protocol Vehicle { func speed() -> Int }

D. protocol Vehicle { let speed: Int }

Solution

1. Step 1: Understand property requirements in protocols

   To require a property to be readable and writable, use { get set } in the protocol.

2. Step 2: Analyze each option

   protocol Vehicle { var speed: Int { get set } } correctly declares speed as a variable property with get set. protocol Vehicle { var speed: Int } misses get set, so it's read-only. protocol Vehicle { func speed() -> Int } declares a method, not a property. protocol Vehicle { let speed: Int } uses let, which is not allowed in protocols.

3. Final Answer:

   protocol Vehicle { var speed: Int { get set } } -> Option A

4. Quick Check:

   Writable property = var with get set [OK]

Hint: Use 'var' with { get set } for read-write properties [OK]

Common Mistakes:

• Using 'let' in protocol properties
• Omitting { get set } for writable properties
• Confusing methods with properties