Swift代理方法反向传值

//  AppDelegate.swift
//  ReverseSendValue
import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        let first=FirstViewController()
        first.view.backgroundColor=UIColor.whiteColor()
        let navi=UINavigationController(rootViewController: first)
        window?.rootViewController=navi
        return true
    }
}

//  FirstViewController.swift
//  ReverseSendValue
import UIKit
//屏幕尺寸
let kWidth=UIScreen.mainScreen().bounds.size.width
let kHeight=UIScreen.mainScreen().bounds.size.height
//遵守SecondViewControllerDelegate协议
class FirstViewController: UIViewController,SecondViewControllerDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        //搭建视图
        createUI()
    }
    //搭建视图
    func createUI(){
        let frame=CGRectMake(UIScreen.mainScreen().bounds.size.width/2-120, 200, 240, 50)
        let resultLb=UILabel(frame: frame)
        resultLb.text="[email protected]"
        resultLb.textAlignment=NSTextAlignment.Center
        self.view.addSubview(resultLb)
        resultLb.tag=100
        let btn=UIButton()
        btn.frame=CGRectMake(kWidth/2-40, CGRectGetMaxY(resultLb.frame)+20, 100, 40)
        btn.setTitle("修 改", forState: .Normal)
        btn.backgroundColor=UIColor.blueColor()
        btn.addTarget(self, action: Selector("gotoChangeValue"), forControlEvents: .TouchUpInside)
        self.view.addSubview(btn)
    }
    //跳转到修改的视图
    func gotoChangeValue(){
        let second=SecondViewController()
        let lb=self.view.viewWithTag(100) as! UILabel
        second.text=lb.text
        //设置代理
        second.delegate=self
        self.navigationController?.pushViewController(second, animated: true)
    }
    //代理方法
    func sendValue(value:String?){
        let lb=self.view.viewWithTag(100) as! UILabel
        lb.text=value
    }
}

//  SecondViewController.swift
//  ReverseSendValue
import UIKit
//协议
protocol SecondViewControllerDelegate{
    //协议方法
    func sendValue(value:String?)
}
class SecondViewController: UIViewController {
    var text:String?
    //代理属性
    var delegate:SecondViewControllerDelegate?
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor=UIColor.whiteColor()
        //搭建界面
        createUI()
    }
    //搭建界面
    func createUI(){
        let textField=UITextField()
        textField.frame=CGRectMake(kWidth/2-120, 200, 240, 50)
        textField.text=text
        textField.borderStyle=UITextBorderStyle.RoundedRect
        textField.keyboardType=UIKeyboardType.EmailAddress
        textField.textAlignment=NSTextAlignment.Center
        self.view.addSubview(textField)
        textField.tag=101
        let btn=UIButton()
        btn.frame=CGRectMake(UIScreen.mainScreen().bounds.size.width/2-40, CGRectGetMaxY(textField.frame)+20, 100, 40)
        btn.setTitle("修改完成", forState: .Normal)
        btn.backgroundColor=UIColor.orangeColor()
        btn.addTarget(self, action: Selector("doneAction"), forControlEvents: .TouchUpInside)
        self.view.addSubview(btn)
    }
    //完成修改
    func doneAction(){
        let tf=self.view.viewWithTag(101) as! UITextField
        if((delegate) != nil)
        {
            delegate?.sendValue(tf.text)
            self.navigationController?.popViewControllerAnimated(true)
        }
    }
    //隐藏键盘
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        self.view.endEditing(true)
    }
}