Error handling for network calls in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function that fetches data from a URL.

iOS Swift

func fetchData(from url: URL, completion: @escaping (Result<Data, Error>) -> Void) [1]

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

Aasync {

B-> Void {

Cthrows {

D{

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'throws' without marking the function as throwing.

Using 'async' without async context.

Adding '-> Void {' which is redundant here.

The function body starts with an opening brace '{'.

2fill in blank

medium

Complete the code to create a URLSession data task with error handling.

iOS Swift

let task = URLSession.shared.dataTask(with: url) { data, response, error in
    if let [1] = error {
        completion(.failure(error))
        return
    }
}

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

Aerror

Bdata

Cresponse

Durl

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'data' or 'response' instead of 'error'.

Not unwrapping the optional error properly.

We check if 'error' is not nil to handle errors from the network call.

3fill in blank

hard

Fix the error in the code to safely unwrap data and call completion with success.

iOS Swift

guard let [1] = data else {
    completion(.failure(NSError(domain: "", code: -1, userInfo: nil)))
    return
}
completion(.success(data))

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

Aerror

Bresponse

Cdata

Durl

Attempts:

3 left

💡 Hint

Common Mistakes

Unwrapping 'response' or 'error' instead of 'data'.

Passing the optional 'data' directly without unwrapping.

We unwrap 'data' to ensure it is not nil before using it.

4fill in blank

hard

Fill both blanks to start the task and resume it.

iOS Swift

let task = URLSession.shared.dataTask(with: url) { data, response, error in
    // handle response
}
task[1][2]

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

A.

Bstart()

Cresume()

Dbegin()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start()' which does not exist.

Forgetting the dot before the method call.

The task is started by calling 'task.resume()'.

5fill in blank

hard

Fill all three blanks to complete a function that fetches data and handles errors properly.

iOS Swift

func fetchData(from url: URL, completion: @escaping (Result<Data, Error>) -> Void) {
    let task = URLSession.shared.dataTask(with: url) { data, response, error in
        if let [1] = error {
            completion(.failure(error))
            return
        }
        guard let [2] = data else {
            completion(.failure(NSError(domain: "", code: -1, userInfo: nil)))
            return
        }
        completion(.success([3]))
    }
    task.resume()
}

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

Aerror

Bdata

Dresponse

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names for unwrapping.

Passing optional 'data' without unwrapping.

We unwrap 'error' to check for errors, unwrap 'data' to ensure data exists, and pass 'data' to success.