//  ViewController.swift

//  Block

import UIKit

class ViewController: UIViewController {

    var myLabel = UILabel()

    override func viewDidLoad() {

        super.viewDidLoad()

        self.view.backgroundColor = UIColor.whiteColor()

        let btn = UIButton()

        btn.frame = CGRectMake(, , , )

        btn.backgroundColor = UIColor.cyanColor()

        btn.setTitle("下一页", forState: UIControlState.Normal)

        btn.setTitleColor(UIColor.whiteColor(), forState: UIControlState.Normal)

        btn.addTarget(self, action: #selector(ViewController.nextBtnClicked), forControlEvents: UIControlEvents.TouchUpInside)

        self.view.addSubview(btn)

        myLabel.frame = CGRectMake(, , , )

        myLabel.text = "Closure"

        myLabel.textAlignment = NSTextAlignment.Center

        self.view.addSubview(myLabel)

    }

    func someFunctionThatTakesAClosure(string:String) -> Void {

        myLabel.text = string

    }

    func nextBtnClicked(){

        let second = SecondViewController()

        //将当前someFunctionThatTakesAClosure函数指针传到第二个界面，第二个界面的闭包拿到该函数指针后会进行回调该函数

        second.initWithClosure(someFunctionThatTakesAClosure)

        second.BtnName = "点我点我点我"

        self.presentViewController(second, animated: true) {

        }

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // Dispose of any resources that can be recreated.

    }

}

//  SecondViewController.swift

//  Block

import UIKit

typealias sendValueClosure=(string:String)->Void

class SecondViewController: UIViewController {

    var BtnName : String = String()

    var i:Int?

    //声明一个闭包

    var myClosure:sendValueClosure?

    //下面这个方法需要传入上个界面的someFunctionThatTakesAClosure函数指针

    func initWithClosure(closure:sendValueClosure?){

        //将函数指针赋值给myClosure闭包，该闭包中涵盖了someFunctionThatTakesAClosure函数中的局部变量等的引用

        myClosure = closure

    }

    override func viewDidLoad() {

        super.viewDidLoad()

        self.view.backgroundColor = UIColor.whiteColor()

        i =

        let btn = UIButton()

        btn.backgroundColor = UIColor.cyanColor()

        btn.frame = CGRectMake(,,,)

        let string : String = "点击我"

        if BtnName.characters.count ==  {

            BtnName = string

        }

        btn.setTitle(BtnName ,forState:UIControlState.Normal)

        btn.setTitleColor(UIColor.whiteColor(), forState: UIControlState.Normal)

        btn.addTarget(self,action:#selector(SecondViewController.action), forControlEvents:UIControlEvents.TouchUpInside)

        self.view.addSubview(btn)

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // Dispose of any resources that can be recreated.

    }

    func action(){

        i = i!+

        //判空

        if (myClosure != nil){

            //闭包隐式调用someFunctionThatTakesAClosure函数：回调。

            myClosure!(string: "好好哦\(i)")

        }

        self.dismissViewControllerAnimated(true, completion: nil)

    }

}