Protocols/Delegates in Swift - Sample

MyConnection.swift

import Foundation

@objc public protocol MyConnectionDelegate {
    optional func didStartService(object: String)
    optional func didFinishDownload(jsonData: NSData)
    optional func didFailedDownload()
}

public class MyConnection {
    weak public var delegate: MyConnectionDelegate?
    
    public func callService() {
        let url = NSURL(string: "http://cbld.zanec.com/user/countriesList")
        let request = NSURLRequest(URL: url!)
        self.delegate?.didStartService?("Started")

        let session = NSURLSession.sharedSession()
        let task = session.dataTaskWithRequest(request) { (jsonData, response, error) -> Void in
            if (error != nil) {
                self.delegate?.didFailedDownload?()
            } else {
                self.delegate?.didFinishDownload?(jsonData!)
            }
        }
        task.resume()
    }
}

ViewController.swift

class ViewController: UIViewController, MyConnectionDelegate  {

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        let connection = MyConnection()
        connection.delegate = self
        connection.callService()
    }
    
    func didFinishDownload(jsonData: NSData) {
        do {
            let countryDict: NSDictionary = try NSJSONSerialization.JSONObjectWithData(jsonData, options: NSJSONReadingOptions.AllowFragments) as! NSDictionary
            countries = (countryDict["countryList"] as? [NSDictionary])!
        } catch {
            
        }
    }
    
    func didStartService(object: String) {
        print(object)
    }
    

}