POST request with JSON body in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you send a POST request with JSON body in Swift?

You create a POST request in Swift with a JSON body. What is the expected behavior when the request is sent?

iOS Swift

let url = URL(string: "https://example.com/api")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
let json: [String: Any] = ["name": "John", "age": 30]
request.httpBody = try? JSONSerialization.data(withJSONObject: json)

let task = URLSession.shared.dataTask(with: request) { data, response, error in
  if let error = error {
    print("Error: \(error)")
  } else if let data = data {
    print("Response data received")
  }
}
task.resume()

A The server receives a POST request with a JSON body containing the name and age data.

B The server receives a GET request with URL parameters instead of a JSON body.

C The request fails because JSONSerialization cannot convert the dictionary to data.

D The request sends an empty body because httpBody is not set correctly.

💡 Hint

Check the httpMethod and httpBody properties of the URLRequest.

Setting httpMethod to "POST" and httpBody to JSON data sends a POST request with the JSON body to the server.

📝 Syntax

intermediate

Which code snippet correctly sets the JSON body for a POST request in Swift?

Choose the code snippet that correctly sets a JSON body for a POST request using URLRequest in Swift.

A request.httpBody = try? JSONSerialization.data(withJSONObject: ["key": "value"])

B request.httpBody = JSONSerialization.jsonObject(with: ["key": "value"])

C request.httpBody = Data(["key": "value"])

D request.httpBody = "{\"key\":\"value\"}"

💡 Hint

Look for the method that converts a dictionary to Data.

JSONSerialization.data(withJSONObject:) converts a dictionary to JSON Data. The other options are invalid or incorrect types.

❓ lifecycle

advanced

What happens if you forget to call resume() on the URLSession data task?

Consider this Swift code creating a POST request with JSON body but missing a call. What is the effect?

let task = URLSession.shared.dataTask(with: request) { data, response, error in
  // handle response
}

A The request is sent automatically without calling resume().

B The request is never sent because resume() was not called on the task.

C The app crashes with a runtime error.

D The request sends but the completion handler is never called.

💡 Hint

Check how URLSession tasks start their work.

URLSession data tasks start only after calling resume(). Without it, the task is created but never runs.

🔧 Debug

advanced

Why does this POST request with JSON body fail to send data?

Review this Swift code snippet. The POST request is sent but the server receives no JSON data. What is the likely cause?

var request = URLRequest(url: URL(string: "https://api.example.com")!)
request.httpMethod = "POST"
let json = ["user": "alice"]
request.httpBody = try? JSONSerialization.data(withJSONObject: json)
// Missing Content-Type header
let task = URLSession.shared.dataTask(with: request) { data, response, error in
  // handle response
}
task.resume()

A The URL is invalid, so the request fails silently.

B The httpMethod is not set to POST, so the body is ignored.

C JSONSerialization.data(withJSONObject:) throws an error and returns nil.

D The Content-Type header is missing, so the server does not recognize the body as JSON.

💡 Hint

Check the HTTP headers required for JSON data.

Without setting "Content-Type" to "application/json", the server may ignore or reject the JSON body.

🧠 Conceptual

expert

What is the correct way to handle JSON encoding errors in a POST request in Swift?

You want to send a POST request with a JSON body. How should you handle possible errors during JSON encoding?

A Use try? to convert JSON to Data and send the request only if data is not nil.

B Use try! to force JSON encoding and crash if it fails.

C Use a do-catch block to catch encoding errors and handle them gracefully before sending.

D Ignore errors and send an empty body if encoding fails.

💡 Hint

Think about safe error handling in Swift.

Using do-catch allows you to catch and handle JSON encoding errors properly before sending the request.