Why API integration connects to servers in iOS Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a URL session for API calls.

iOS Swift

let session = URLSession[1]

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

A.main

B.background

C.default

D.shared

Attempts:

3 left

💡 Hint

Common Mistakes

Using .default or .main instead of .shared causes errors.

The URLSession.shared is the shared singleton session used for simple API calls.

2fill in blank

medium

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

CurlString

DURL(string: "https://api.example.com/data")

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a variable name without quotes or a URL object instead of a string.

The URL initializer requires a string literal or variable wrapped in quotes.

3fill in blank

hard

Fix the error in the code to start a data task.

iOS Swift

let task = session.dataTask(with: url) { data, response, error in
  guard error == [1] else { return }
  // process data
}
task.resume()

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

A0

Btrue

Cnil

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Checking error == true or error == false causes logic errors.

When there is no error, the error variable is nil.

4fill in blank

hard

Fill both blanks to parse JSON data safely.

iOS Swift

if let data = data {
  let json = try? JSONSerialization.[1](with: data, options: [2])
  // use json
}

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

AjsonObject

BjsonArray

C.allowFragments

DmutableContainers

Attempts:

3 left

💡 Hint

Common Mistakes

Using jsonArray instead of jsonObject or wrong options causes parsing errors.

Use jsonObject to parse JSON and .allowFragments to allow top-level fragments.

5fill in blank

hard

Fill all three blanks to send a GET request with URLRequest.

iOS Swift

var request = URLRequest(url: [1])
request.httpMethod = [2]
request.addValue([3], forHTTPHeaderField: "Content-Type")

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

Aurl

B"GET"

C"application/json"

D"POST"

Attempts:

3 left

💡 Hint

Common Mistakes

Using "POST" instead of "GET" or wrong header values.

Use the URL variable for the request URL, set method to "GET", and content type to "application/json".

Practice

1. Why does an iOS app use API integration to connect to servers?

easy

A. To speed up the app without internet

B. To change the app's color scheme locally

C. To increase the app's storage on the device

D. To get or send data like live updates or user info

Solution

1. Step 1: Understand the purpose of API integration

   API integration allows the app to communicate with servers to exchange data.

2. Step 2: Identify what connecting to servers achieves

   This connection helps the app get live information or save user actions online.

3. Final Answer:

   To get or send data like live updates or user info -> Option D

4. Quick Check:

   API integration = data exchange with servers [OK]

Hint: API integration means data exchange with servers [OK]

Common Mistakes:

• Thinking API changes app colors locally
• Believing API increases device storage
• Assuming API speeds app without internet

2. Which Swift code snippet correctly starts a simple API request to a server?

easy

A. URLSession.shared.dataTask(url) { data, response in print(data) }

B. let task = URLSession.shared.dataTask(with: url) { data, _, _ in print(data) }
task.resume()

C. URLSession.shared.request(url) { response in print(response) }

D. let task = URLSession.dataTask(url) { data in print(data) }
task.start()

Solution

1. Step 1: Check correct URLSession method usage

   The correct method is URLSession.shared.dataTask(with: url) with a completion handler.

2. Step 2: Confirm how to start the task

   The task must be started by calling task.resume() to begin the request.

3. Final Answer:

   let task = URLSession.shared.dataTask(with: url) { data, _, _ in print(data) } task.resume() -> Option B

4. Quick Check:

   Correct URLSession syntax = let task = URLSession.shared.dataTask(with: url) { data, _, _ in print(data) } task.resume() [OK]

Hint: Use URLSession.shared.dataTask(with:) and call resume() [OK]

Common Mistakes:

• Forgetting to call resume() to start the task
• Using wrong method names like request()
• Incorrect closure parameters in dataTask

3. What will this Swift code print if the server returns JSON data successfully?

let url = URL(string: "https://api.example.com/data")!
let task = URLSession.shared.dataTask(with: url) { data, _, error in
  if let data = data {
    print(String(data: data, encoding: .utf8) ?? "No data")
  } else {
    print("Error")
  }
}
task.resume()

medium

A. The JSON data as a string

B. Error

C. nil

D. Nothing prints

Solution

1. Step 1: Analyze the dataTask completion handler

   If data is received, it converts data to a UTF-8 string and prints it.

2. Step 2: Understand the output when server returns JSON

   The JSON data bytes convert to a readable string and print to console.

3. Final Answer:

   The JSON data as a string -> Option A

4. Quick Check:

   Data received = print JSON string [OK]

Hint: If data exists, it prints as string [OK]

Common Mistakes:

• Assuming print("Error") always runs
• Expecting nil instead of string output
• Thinking nothing prints without resume()

4. Identify the error in this Swift code for API integration:

let url = URL(string: "https://api.example.com")
let task = URLSession.shared.dataTask(with: url!) { data, response, error in
  if error != nil {
    print("Failed")
  } else {
    print("Success")
  }
}

medium

A. Closure parameters are incorrect

B. URL string is invalid

C. Missing task.resume() to start the request

D. Using URLSession.shared incorrectly

Solution

1. Step 1: Check if the data task is started

   The code creates the task but never calls task.resume(), so the request never runs.

2. Step 2: Confirm other parts are correct

   The URL is valid, closure parameters match, and URLSession usage is correct.

3. Final Answer:

   Missing task.resume() to start the request -> Option C

4. Quick Check:

   Without resume(), request won't run [OK]

Hint: Always call resume() to start URLSession tasks [OK]

Common Mistakes:

• Forgetting to call resume()
• Force unwrapping URL without checking
• Misnaming closure parameters

5. You want your app to fetch user profile data from a server and update the UI only after the data arrives. Which approach correctly handles this API integration in Swift?

hard

A. Use URLSession dataTask with a completion handler, then update UI on the main thread inside the handler

B. Call URLSession dataTask and update UI immediately after task creation

C. Fetch data synchronously on the main thread to block UI until data arrives

D. Use URLSession dataTask without a completion handler and update UI later

Solution

1. Step 1: Understand asynchronous data fetching

   URLSession dataTask runs asynchronously; UI updates must happen after data arrives.

2. Step 2: Ensure UI updates happen on main thread

   Inside the completion handler, dispatch UI updates to the main thread to avoid errors.

3. Final Answer:

   Use URLSession dataTask with a completion handler, then update UI on the main thread inside the handler -> Option A

4. Quick Check:

   Async fetch + main thread UI update = Use URLSession dataTask with a completion handler, then update UI on the main thread inside the handler [OK]

Hint: Update UI on main thread inside completion handler [OK]

Common Mistakes:

• Updating UI before data arrives
• Blocking main thread with synchronous calls
• Ignoring main thread for UI updates