GET request with async/await in iOS Swift

Introduction

We use GET requests to ask a server for information. Using async/await makes this easy and clear without blocking the app.

When you want to load user data from a website.

When your app needs to show the latest news or weather.

When fetching images or text from the internet to display.

When you want to update your app content without freezing the screen.

Syntax

iOS Swift

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

async means the function runs without blocking the app.

await waits for the network call to finish before continuing.

Examples

This example fetches plain text from a URL and converts it to a String.

iOS Swift

func fetchText() async throws -> String {
  let url = URL(string: "https://example.com/text.txt")!
  let (data, _) = try await URLSession.shared.data(from: url)
  return String(decoding: data, as: UTF8.self)
}

This example fetches JSON data and converts it into a dictionary.

iOS Swift

func fetchJSON() async throws -> [String: Any] {
  let url = URL(string: "https://example.com/info.json")!
  let (data, _) = try await URLSession.shared.data(from: url)
  let json = try JSONSerialization.jsonObject(with: data) as? [String: Any]
  return json ?? [:]
}

Sample App

This SwiftUI app fetches a to-do item from the internet using async/await. It shows the task title on screen or an error message if something goes wrong.

iOS Swift

import SwiftUI

struct ContentView: View {
  @State private var message = "Loading..."

  var body: some View {
    Text(message)
      .padding()
      .task {
        do {
          let url = URL(string: "https://jsonplaceholder.typicode.com/todos/1")!
          let (data, _) = try await URLSession.shared.data(from: url)
          if let todo = try? JSONDecoder().decode(Todo.self, from: data) {
            message = "Task: \(todo.title)"
          } else {
            message = "Failed to decode data"
          }
        } catch {
          message = "Error: \(error.localizedDescription)"
        }
      }
  }
}

struct Todo: Codable {
  let userId: Int
  let id: Int
  let title: String
  let completed: Bool
}

@main
struct MyApp: App {
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

Important Notes

Always check for errors using do-catch when using async/await with network calls.

Use URLSession.shared.data(from:) for simple GET requests.

Remember to update UI on the main thread; SwiftUI's .task modifier handles this automatically.

Summary

GET requests ask a server for data.

async/await makes network calls easy and keeps the app responsive.

Use URLSession.shared.data(from:) with await to get data.

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