Swift 协议和委托，代理

协议 (Protocols)

用于统一方法和属性的名称，而不实现任何功能，能够被类、枚举、结构体实现，满足协议要求的都成为协议的遵循者，遵循者需要提供协议指定的成员，如方法，属性，操作符，下标

语法

protocol SomeProtocol {

// protocol definition goes here

}

// 中间以冒号分隔实现协议，有多个协议的话，协议之间逗号分隔

struct SomeStructure: FirstProtocol, AnotherProtocol {

// structure definition goes here

}

// 含有父类的同时实现协议，父类写在协议之前

class SomeClass: SomeSuperclass, FirstProtocol, AnotherProtocol {

// class definition goes here

}

委托(代理)模式

委托是一种设计模式，它允许类或结构体将一些需要它们负责的功能交由(委托)给其他的类型。

委托模式的实现很简单： 定义协议来封装那些需要被委托的函数和方法， 使其遵循者拥有这些被委托的函数和方法。

委托模式可以用来响应特定的动作或接收外部数据源提供的数据，而无需要知道外部数据源的类型

语法

FirstViewController的代码

class FirstViewController: UIViewController, SecondViewControllerDelegate {

    @IBOutlet weak var showDelegateTextLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
    
    //点击按钮跳转到SecondViewController
    @IBAction func tapGoSecondViewController(sender: UIButton) {
        //从storyboard上加载SecondViewController
        let secondVC = UIStoryboard(name: "Main", bundle: NSBundle.mainBundle()).instantiateViewControllerWithIdentifier("secondViewController") as! SecondViewController
      
        secondVC.delegate = self
        //跳转到SecondViewController
        self.navigationController?.pushViewController(secondVC, animated: true)
    }
    //MARK: - SecondViewControllerDelegate
    func fetchBackString(str: String) {
        self.showDelegateTextLabel.text = str
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

SecondViewController的代码

import UIKit


protocol SecondViewControllerDelegate: NSObjectProtocol{
    func fetchBackString(str: String)
}

class SecondViewController: UIViewController {
    
    @IBOutlet weak var inputTextField: UITextField!
    
    weak var delegate: SecondViewControllerDelegate?
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    @IBAction func delegateBackMethod(sender: UIButton) {
        if self.delegate != nil {
            if let tempString = self.inputTextField.text {
                delegate!.fetchBackString("代理返回数据:\(tempString)")
            }
        }
        self.navigationController?.popViewControllerAnimated(true)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}