URLSession is a powerful API provided by Apple for handling HTTP requests in iOS, macOS, watchOS, and tvOS applications. It is an essential tool for developers who need to interact with web services, download files, or upload data. Understanding how to use URLSession effectively can significantly enhance the performance and reliability of your networked applications.

In this article, we will explore how to create and use URLSession in Swift. We will cover the basics of making GET and POST requests, handling responses, and managing errors. By the end of this guide, you will have a solid understanding of how to implement network operations using URLSession in your Apple environment.

Examples:

1. Making a Simple GET Request

import Foundation

// Define the URL
let url = URL(string: "https://jsonplaceholder.typicode.com/posts/1")!

// Create a URLSession
let session = URLSession.shared

// Create a data task
let task = session.dataTask(with: url) { data, response, error in
    // Check for errors
    if let error = error {
        print("Error: \(error)")
        return
    }

    // Ensure we have data
    guard let data = data else {
        print("No data")
        return
    }

    // Parse the JSON
    do {
        if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] {
            print("JSON Response: \(json)")
        }
    } catch {
        print("Error parsing JSON: \(error)")
    }
}

// Start the task
task.resume()

2. Making a POST Request

import Foundation

// Define the URL
let url = URL(string: "https://jsonplaceholder.typicode.com/posts")!

// Create a URLRequest
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")

// Define the body data
let body: [String: Any] = ["title": "foo", "body": "bar", "userId": 1]
let bodyData = try! JSONSerialization.data(withJSONObject: body, options: [])

// Set the body data
request.httpBody = bodyData

// Create a URLSession
let session = URLSession.shared

// Create a data task
let task = session.dataTask(with: request) { data, response, error in
    // Check for errors
    if let error = error {
        print("Error: \(error)")
        return
    }

    // Ensure we have data
    guard let data = data else {
        print("No data")
        return
    }

    // Parse the JSON
    do {
        if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] {
            print("JSON Response: \(json)")
        }
    } catch {
        print("Error parsing JSON: \(error)")
    }
}

// Start the task
task.resume()

3. Handling Errors

import Foundation

// Define the URL
let url = URL(string: "https://jsonplaceholder.typicode.com/posts/1")!

// Create a URLSession
let session = URLSession.shared

// Create a data task
let task = session.dataTask(with: url) { data, response, error in
    // Check for errors
    if let error = error {
        print("Error: \(error.localizedDescription)")
        return
    }

    // Check the response status code
    if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode != 200 {
        print("HTTP Status Code: \(httpResponse.statusCode)")
        return
    }

    // Ensure we have data
    guard let data = data else {
        print("No data")
        return
    }

    // Parse the JSON
    do {
        if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] {
            print("JSON Response: \(json)")
        }
    } catch {
        print("Error parsing JSON: \(error)")
    }
}

// Start the task
task.resume()