POST request with JSON body in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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"

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

Chttps://api.example.com/data

DurlString

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around the URL string.

Passing a variable name without quotes if it's not defined.

The URL initializer requires a string literal or variable of type String. The string must be quoted.

2fill in blank

medium

Complete the code to set the HTTP method to POST.

iOS Swift

var request = URLRequest(url: url)
request.httpMethod = [1]

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

A"POST"

B"GET"

CPOST

Dpost

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase method names without quotes.

Passing the method name without quotes.

The httpMethod property expects a string with the HTTP method name in uppercase and quotes.

3fill in blank

hard

Fix the error in setting the Content-Type header for JSON.

iOS Swift

request.setValue([1], forHTTPHeaderField: "Content-Type")

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

Aapplication/json

Bjson

C"application/json"

D"application/xml"

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted strings.

Using wrong MIME types like application/xml.

The Content-Type header value must be a string with the exact MIME type for JSON, quoted.

4fill in blank

hard

Fill both blanks to encode a dictionary as JSON data and assign it to the request body.

iOS Swift

let json: [String: Any] = ["name": "John", "age": 30]
request.httpBody = try? JSONSerialization.[1](withJSONObject: json, options: .[2])

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

Adata

BjsonObject

CprettyPrinted

DfragmentsAllowed

Attempts:

3 left

💡 Hint

Common Mistakes

Using jsonObject instead of data method.

Passing invalid options.

The method to convert JSON to Data is 'data', and 'prettyPrinted' is a valid option for formatting.

5fill in blank

hard

Fill all three blanks to create a URLSession data task that sends the request and handles the response.

iOS Swift

let task = URLSession.shared.dataTask(with: request) { data, response, error in
  guard let [1] = data, error == nil else { return }
  if let httpResponse = response as? [2], httpResponse.statusCode == [3] {
    print("Success")
  }
}
task.resume()

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

AresponseData

BHTTPURLResponse

C200

DURLResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Using URLResponse instead of HTTPURLResponse for statusCode.

Using wrong status code numbers.

The data is assigned to a variable (responseData), the response cast to HTTPURLResponse, and 200 is the success status code.

Practice

1. What is the main purpose of a POST request with a JSON body in iOS Swift networking?

easy

A. To send data to a server, usually to create or update resources

B. To retrieve data from a server without sending any data

C. To delete data from a server

D. To open a WebSocket connection

Solution

1. Step 1: Understand HTTP methods

   POST requests are used to send data to a server, often to create or update something.

2. Step 2: Recognize JSON role

   JSON is a format to structure the data sent in the body of the POST request.

3. Final Answer:

   To send data to a server, usually to create or update resources -> Option A

4. Quick Check:

   POST sends data = A [OK]

Hint: POST means send data to server, not just get [OK]

Common Mistakes:

• Confusing POST with GET method
• Thinking POST is for deleting data
• Ignoring the role of JSON in the body

2. Which Swift code snippet correctly sets the HTTP method to POST and adds a JSON Content-Type header?

easy

A. request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")

B. request.method = "POST"
request.addHeader("Content-Type", value: "application/json")

C. request.httpMethod = POST
request.setHeader("Content-Type", "application/json")

D. request.method = POST
request.setValue("json", forHTTPHeaderField: "Content-Type")

Solution

1. Step 1: Set HTTP method correctly

   The property to set HTTP method in URLRequest is httpMethod and it expects a String like "POST".

2. Step 2: Add JSON Content-Type header properly

   Use setValue(_:forHTTPHeaderField:) with "application/json" for the "Content-Type" header.

3. Final Answer:

   request.httpMethod = "POST"\nrequest.setValue("application/json", forHTTPHeaderField: "Content-Type") -> Option A

4. Quick Check:

   Correct method and header syntax = A [OK]

Hint: Use request.httpMethod and setValue for headers [OK]

Common Mistakes:

• Using wrong property names like method or setHeader
• Forgetting quotes around "POST"
• Using incorrect header field names or values

3. Given the Swift code below, what will be the printed output?

let url = URL(string: "https://example.com/api")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
let jsonBody = ["name": "Alice", "age": 30] as [String : Any]
request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody)
print(String(data: request.httpBody!, encoding: .utf8)!)

medium

A. ["name": "Alice", "age": 30]

B. {"name":"Alice","age":30}

C. Optional({"name":"Alice","age":30})

D. nil

Solution

1. Step 1: Serialize dictionary to JSON data

   JSONSerialization.data converts the dictionary to JSON data bytes representing {"name":"Alice","age":30}.

2. Step 2: Convert data to UTF-8 string

   Printing the data as UTF-8 string shows the JSON string without brackets or Optional wrapper.

3. Final Answer:

   {"name":"Alice","age":30} -> Option B

4. Quick Check:

   JSONSerialization outputs JSON string = B [OK]

Hint: JSONSerialization outputs JSON string, not Swift dictionary syntax [OK]

Common Mistakes:

• Expecting Swift dictionary syntax instead of JSON string
• Printing Optional wrapper
• Forgetting to unwrap data or encoding

4. Identify the error in this Swift code for sending a POST request with JSON body:

var request = URLRequest(url: URL(string: "https://api.example.com")!)
request.httpMethod = "POST"
let json = ["key": "value"]
request.httpBody = try? JSONSerialization.jsonObject(with: json)

medium

A. httpMethod should be lowercase "post"

B. Missing setting Content-Type header to application/json

C. Using JSONSerialization.jsonObject instead of data(withJSONObject:)

D. URLRequest initialization is incorrect

Solution

1. Step 1: Check JSON serialization method

   jsonObject(with:) parses JSON data to object; to create JSON data from object, use data(withJSONObject:).

2. Step 2: Confirm other parts

   Content-Type header missing is an issue but not the main error causing failure here.

3. Final Answer:

   Using JSONSerialization.jsonObject instead of data(withJSONObject:) -> Option C

4. Quick Check:

   Wrong JSON method used = D [OK]

Hint: Use data(withJSONObject:) to create JSON data, not jsonObject(with:) [OK]

Common Mistakes:

• Confusing jsonObject(with:) with data(withJSONObject:)
• Forgetting Content-Type header
• Incorrect URLRequest initialization

5. You want to send a POST request with a JSON body containing user info, but only include the "email" field if it is not empty. Which Swift code snippet correctly creates the JSON body for this conditional inclusion?

hard

A. var jsonBody = ["name": "Bob", "email": email]
if !email.isEmpty {
jsonBody.removeValue(forKey: "email")
}
request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody)

B. let jsonBody = ["name": "Bob", "email": email.isEmpty ? nil : email]
request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody)

C. let jsonBody = ["name": "Bob"]
if email != "" {
jsonBody["email"] = email
}
request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody)

D. var jsonBody = ["name": "Bob"]
if !email.isEmpty {
jsonBody["email"] = email
}
request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody)

Solution

1. Step 1: Understand conditional dictionary update

   var jsonBody = ["name": "Bob"] if !email.isEmpty { jsonBody["email"] = email } request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody) creates a mutable dictionary and adds "email" only if not empty, which is correct.

2. Step 2: Check other options for errors

   let jsonBody = ["name": "Bob", "email": email.isEmpty ? nil : email] request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody) uses nil in dictionary literal which is invalid; var jsonBody = ["name": "Bob", "email": email] if !email.isEmpty { jsonBody.removeValue(forKey: "email") } request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody) uses inverted condition, removing email when it is not empty, incorrect; let jsonBody = ["name": "Bob"] if email != "" { jsonBody["email"] = email } request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody) tries to mutate immutable dictionary.

3. Final Answer:

   var jsonBody = ["name": "Bob"]\nif !email.isEmpty {\n jsonBody["email"] = email\n}\nrequest.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody) -> Option D

4. Quick Check:

   Mutable dict + conditional add = C [OK]

Hint: Use var dictionary and add keys conditionally [OK]

Common Mistakes:

• Using let dictionary and trying to mutate it
• Including nil values in dictionary literal
• Adding then removing keys instead of conditional add