URLSession basics in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you call resume() on a URLSessionDataTask?

You create a URLSessionDataTask but forget to call resume(). What will happen?

A The task will never start and no data will be fetched.

B The app will crash with a runtime error.

C The task will start immediately and fetch data.

D The task will start but complete with an error.

💡 Hint

Think about what resume() does for a URLSessionDataTask.

URLSessionDataTask starts in a suspended state. You must call resume() to start it. Without resume(), the task stays suspended and does nothing.

🧠 Conceptual

intermediate

What is the role of the completion handler in URLSession dataTask?

Why do we provide a completion handler when creating a dataTask with URLSession?

A To configure the request headers before sending.

B To automatically retry the request on failure.

C To cancel the task if it takes too long.

D To handle the response data, response, and error after the request finishes.

💡 Hint

Think about what happens after the network call completes.

The completion handler runs after the network request finishes. It provides the data received, the server response, and any error that occurred.

📝 Syntax

advanced

Which code snippet correctly creates and starts a URLSession data task?

Select the code that correctly creates a data task to fetch data from a URL and starts it.

iOS Swift

let url = URL(string: "https://example.com")!
let task = URLSession.shared.dataTask(with: url) { data, response, error in
  // handle response
}
// What is missing here?

A task.run()

B task.resume()

C task.begin()

D task.start()

💡 Hint

Look for the method that starts the task.

The correct method to start a URLSessionDataTask is resume(). Other methods do not exist and cause errors.

❓ lifecycle

advanced

What happens if you call resume() twice on the same URLSessionDataTask?

Consider this code: let task = URLSession.shared.dataTask(with: url) { data, response, error in // handle response } task.resume() task.resume() What is the effect of calling resume() twice?

A The task runs twice and fetches data two times.

B The app crashes with an exception.

C The second resume() call has no effect; the task runs only once.

D The task cancels after the second resume() call.

💡 Hint

Think about the task state after the first resume().

Calling resume() on a running task does nothing. The task runs once and ignores subsequent resume() calls.

🔧 Debug

expert

Why does this URLSession dataTask completion handler never run?

Look at this code: let url = URL(string: "https://example.com")! let task = URLSession.shared.dataTask(with: url) { data, response, error in print("Response received") } // Missing line here Why does "Response received" never print?

A Because the task was never started with resume().

B Because the URL is invalid and the task fails silently.

C Because the completion handler is not called on the main thread.

D Because the URLSession.shared is nil.

💡 Hint

Check if the task is started after creation.

URLSessionDataTask starts suspended. Without calling resume(), the completion handler never runs.