在开发中，经常需要用到协议代理模式。比如，进入编辑页面修改数据后，将新数据回传到主界面。

import UIKit

class ViewController: UIViewController,EditViewControllerDelegate{
    
    @IBOutlet weak var label: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    //页面跳转时
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "EditView"{
            //通过seque的标识获得跳转目标
            let controller = segue.destination as! EditViewController
            //设置代理
            controller.delegate = self
            //将值传递给新页面
            controller.oldInfo = label.text
        }
    }
    
    func editInfo(controller:EditViewController, newInfo:String){
        label.text = newInfo;
        //关闭编辑页面
        controller.presentingViewController!.dismiss(animated: true, completion: nil)
    }
    
    func editInfoDidCancer(controller:EditViewController){
        //关闭编辑页面
        controller.presentingViewController!.dismiss(animated: true, completion: nil)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

4，编辑页 EditViewController.swift

import UIKit

class EditViewController: UIViewController {
    
    @IBOutlet weak var textField: UITextField!
    
    var delegate:EditViewControllerDelegate?
    
    var oldInfo:String?
    
    override func viewDidLoad() {
        super.viewDidLoad()

        if oldInfo  != nil{
            textField.text = oldInfo
        }
    }
    
    @IBAction func done(_ sender: AnyObject) {
        delegate?.editInfo(controller: self, newInfo: textField.text!)
    }
    
    @IBAction func cancel(_ sender: AnyObject) {
        delegate?.editInfoDidCancer(controller: self)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

5，编辑页代理 EditViewControllerDelegate.swift

protocol EditViewControllerDelegate{
    func editInfo(controller:EditViewController, newInfo:String)
    func editInfoDidCancer(controller:EditViewController)
}

6，在Storyboard中，将编辑页的Class设为EditViewController