GET request with async/await in iOS Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does async/await help you do in Swift networking?

Async/await lets you write asynchronous code that looks like normal, easy-to-read code. It helps you wait for network responses without blocking the app.

beginner

Which Swift type is used to make a GET request asynchronously?

URLSession.shared.data(from:) is used with async/await to make GET requests and get data and response.

intermediate

What is the purpose of 'try' in 'let (data, response) = try await URLSession.shared.data(from: url)'?

'Try' is used because the data task can throw an error if the request fails, so you must handle or propagate errors.

intermediate

How do you check if the GET request was successful in Swift?

Check if the response is an HTTPURLResponse and its statusCode is 200 (OK) to confirm success.

beginner

Why is it important to use async/await instead of completion handlers for GET requests?

Async/await makes code easier to read and maintain by avoiding nested closures and callback hell.

Which Swift method is used with async/await to perform a GET request?

A URLSession.shared.data(from:)

B URLSession.shared.downloadTask(with:)

C URLSession.shared.uploadTask(with:)

D URLSession.shared.dataTask(with:completionHandler:)

URLSession.shared.data(from:) is designed for async/await usage to fetch data from a URL.

What keyword do you use to wait for a network call to finish in Swift async/await?

A wait

B await

C pause

D async

'await' pauses the function until the asynchronous call completes.

What does the 'try' keyword indicate in Swift async calls?

A The call might throw an error

B The call will never fail

C The call is synchronous

D The call is optional

'try' means the function can throw an error, so you must handle it.

How do you confirm a successful HTTP GET response in Swift?

A Check if statusCode == 404

B Check if statusCode == 301

C Check if statusCode == 500

D Check if statusCode == 200

Status code 200 means the request was successful.

Why prefer async/await over completion handlers for GET requests?

A Async/await is slower

B Async/await is harder to read

C Async/await avoids nested callbacks

D Async/await requires more code

Async/await makes asynchronous code look simpler and avoids callback nesting.

Explain how to perform a GET request using async/await in Swift.

Think about how to wait for data and handle errors.

Describe why async/await improves code readability compared to completion handlers in networking.

Imagine reading a story versus a maze.

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