POST request with JSON body in iOS Swift

Introduction

We use POST requests with JSON body to send data from your app to a server. This helps you save or update information online.

When a user submits a form like signing up or logging in.

When sending a message or comment to a chat or social app.

When uploading settings or preferences to your account.

When creating a new item like a post, photo, or task in an app.

Syntax

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] = ["key": "value"]
let jsonData = try? JSONSerialization.data(withJSONObject: json)

request.httpBody = jsonData

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

Set the HTTP method to "POST" to tell the server you want to send data.

Set the "Content-Type" header to "application/json" to specify the data format.

Examples

Send login info as JSON in the POST request body.

iOS Swift

var request = URLRequest(url: URL(string: "https://api.example.com/login")!)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")

let body = ["username": "user1", "password": "pass123"]
request.httpBody = try? JSONSerialization.data(withJSONObject: body)

Create a new task by sending its details as JSON.

iOS Swift

var request = URLRequest(url: URL(string: "https://api.example.com/tasks")!)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")

let taskData = ["title": "Buy milk", "done": false] as [String : Any]
request.httpBody = try? JSONSerialization.data(withJSONObject: taskData)

Sample App

This example sends a POST request with a JSON body to a test API. It prints the server's JSON response in the console.

iOS Swift

import UIKit

class ViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    sendPostRequest()
  }

  func sendPostRequest() {
    guard let url = URL(string: "https://jsonplaceholder.typicode.com/posts") else { return }
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")

    let jsonBody: [String: Any] = ["title": "foo", "body": "bar", "userId": 1]
    request.httpBody = try? JSONSerialization.data(withJSONObject: jsonBody)

    let task = URLSession.shared.dataTask(with: request) { data, response, error in
      if let error = error {
        print("Error: \(error.localizedDescription)")
        return
      }
      guard let data = data else {
        print("No data received")
        return
      }
      if let responseJSON = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
        print("Response JSON: \(responseJSON)")
      }
    }
    task.resume()
  }
}

Important Notes

Always set the Content-Type header to "application/json" when sending JSON data.

Use URLSession's dataTask to send the request asynchronously.

Handle errors and check the response to know if the request succeeded.

Summary

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

JSON is a common format to send structured data in the request body.

Set the HTTP method and headers correctly to make the server understand your data.