GET request with async/await in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a URL object from a string.

iOS Swift

guard let url = URL(string: [1]) else { return }

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

A"https://api.example.com/data"

Bhttps://api.example.com/data

CURL("https://api.example.com/data")

DurlString

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put the URL string in quotes.

Passing a variable name that is not defined.

The URL initializer expects a string, so the URL string must be in quotes.

2fill in blank

medium

Complete the code to perform an asynchronous GET request using URLSession.

iOS Swift

let (data, _) = try await URLSession.shared.[1](from: url)

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

AdownloadTask

BdataTask

Cpost

Ddata(from:)

Attempts:

3 left

💡 Hint

Common Mistakes

Using dataTask which is not async/await compatible.

Using downloadTask which downloads to a file.

The async method to get data from a URL is data(from:).

3fill in blank

hard

Fix the error in the async function declaration for fetching data.

iOS Swift

func fetchData() async throws -> Data {
    let url = URL(string: "https://api.example.com/data")!
    let (data, _) = try await URLSession.shared.data(from: url)
    return [1]
}

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

Aurl

Bdata

Cself

Dresponse

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the URL instead of data.

Returning the response object which is not declared.

The function should return the data received from the network call.

4fill in blank

hard

Fill both blanks to decode JSON data into a Swift struct.

iOS Swift

let decoder = JSONDecoder()
let result = try decoder.[1](MyStruct.self, from: [2])

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

Adecode

Bdata

CjsonData

Dencode

Attempts:

3 left

💡 Hint

Common Mistakes

Using encode instead of decode.

Passing wrong variable instead of data.

Use decode method to decode JSON data. The data variable holds the JSON bytes.

5fill in blank

hard

Fill all three blanks to complete the async function that fetches and decodes JSON.

iOS Swift

func fetchAndDecode() async throws -> MyStruct {
    guard let url = URL(string: [1]) else { throw URLError(.badURL) }
    let ([2], _) = try await URLSession.shared.data(from: url)
    let decoder = JSONDecoder()
    return try decoder.decode([3].self, from: data)
}

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

A"https://api.example.com/data"

Bdata

CMyStruct

Durl

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the URL string.

Using wrong variable names for data.

Passing wrong type to decode.

The URL string must be quoted, data holds the downloaded bytes, and MyStruct is the type to decode.

Practice

1. What does the async keyword indicate in a Swift function that performs a GET request?

easy

A. The function is synchronous and blocks the main thread.

B. The function runs asynchronously and can be awaited.

C. The function automatically retries on failure.

D. The function only works with POST requests.

Solution

1. Step 1: Understand async keyword meaning

   The async keyword means the function runs asynchronously, allowing other code to run while waiting.

2. Step 2: Connect async with await usage

   Functions marked async can be called with await to pause until the result is ready without blocking.

3. Final Answer:

   The function runs asynchronously and can be awaited. -> Option B

4. Quick Check:

   async means asynchronous function [OK]

Hint: async means function can be paused with await [OK]

Common Mistakes:

• Thinking async means synchronous/blocking
• Confusing async with retry logic
• Assuming async only applies to POST requests

2. Which of the following is the correct syntax to perform a GET request using async/await in Swift?

easy

A. let (data, _) = try await URLSession.shared.data(from: url)

B. let data = URLSession.shared.dataTask(with: url)

C. let data = await URLSession.shared.data(from: url)

D. let (data, response) = URLSession.shared.data(from: url)

Solution

1. Step 1: Identify correct async/await syntax

   The correct syntax uses try await with URLSession.shared.data(from:) to get data and response.

2. Step 2: Check tuple unpacking

   The method returns a tuple of (Data, URLResponse), so unpacking with (data, _) is correct if response is unused.

3. Final Answer:

   let (data, _) = try await URLSession.shared.data(from: url) -> Option A

4. Quick Check:

   Use try await with data(from:) [OK]

Hint: Use try await with data(from:) and unpack tuple [OK]

Common Mistakes:

• Omitting try keyword
• Using dataTask without await
• Not unpacking the returned tuple

3. Given the code below, what will be printed if the GET request succeeds?

func fetchData() async {
  let url = URL(string: "https://example.com/data.json")!
  do {
    let (data, _) = try await URLSession.shared.data(from: url)
    print("Data length: \(data.count)")
  } catch {
    print("Failed to fetch")
  }
}

medium

A. Syntax error

B. Failed to fetch

C. Data length: 0

D. Data length: [number of bytes in data]

Solution

1. Step 1: Analyze successful GET request

   If the request succeeds, try await returns data and response without throwing an error.

2. Step 2: Understand print statement output

   The code prints the length of the received data in bytes, so output is "Data length: [number]".

3. Final Answer:

   Data length: [number of bytes in data] -> Option D

4. Quick Check:

   Success prints data length [OK]

Hint: Success prints data length, failure prints error [OK]

Common Mistakes:

• Assuming print shows raw data
• Confusing catch block output
• Expecting zero length on success

4. Identify the error in this Swift async GET request code:

func load() async {
  let url = URL(string: "https://api.example.com")!
  let (data, response) = URLSession.shared.data(from: url)
  print(String(data: data, encoding: .utf8) ?? "No data")
}

medium

A. Incorrect print statement syntax

B. URL is invalid

C. Missing await keyword before URLSession.shared.data(from: url)

D. Missing try keyword before URLSession.shared.data(from: url)

Solution

1. Step 1: Check async call usage

   The method data(from:) is async and must be awaited with await.

2. Step 2: Confirm missing await keyword

   The code calls URLSession.shared.data(from: url) without await, causing a compile error.

3. Final Answer:

   Missing await keyword before URLSession.shared.data(from: url) -> Option C

4. Quick Check:

   Async calls require await [OK]

Hint: Async calls always need await keyword [OK]

Common Mistakes:

• Forgetting await on async calls
• Assuming try is optional
• Misreading URL validity

5. You want to fetch JSON data from a URL and decode it into a Swift struct using async/await. Which code snippet correctly performs the GET request and decodes the data?

struct User: Decodable {
  let id: Int
  let name: String
}

func fetchUser() async throws -> User {
  let url = URL(string: "https://api.example.com/user")!
  // Which code goes here?
}

hard

A. let (data, _) = try await URLSession.shared.data(from: url)
return try JSONDecoder().decode(User.self, from: data)

B. let data = try URLSession.shared.data(from: url)
return JSONDecoder().decode(User.self, from: data)

C. let (data, _) = URLSession.shared.data(from: url)
return try JSONDecoder().decode(User.self, from: data)

D. let (data, _) = try await URLSession.shared.dataTask(with: url)
return try JSONDecoder().decode(User.self, from: data)

Solution

1. Step 1: Use async/await with data(from:)

   The correct async call is try await URLSession.shared.data(from: url) which returns data and response.

2. Step 2: Decode JSON data into struct

   Use JSONDecoder().decode(User.self, from: data) to convert JSON bytes into the User struct.

3. Final Answer:

   let (data, _) = try await URLSession.shared.data(from: url) return try JSONDecoder().decode(User.self, from: data) -> Option A

4. Quick Check:

   Use try await with data(from:) and decode JSON [OK]

Hint: Use try await data(from:) then decode JSON [OK]

Common Mistakes:

• Using dataTask instead of data(from:)
• Omitting await or try keywords
• Not decoding JSON properly