{ (parameters/接收的参数) -> (return type/闭包返回值类型) in
  statements/保存在闭包中需要执行的代码
 }

//为没有参数也没有返回值的闭包类型起一个别名
 typealias Nothing = () -> ()

 //如果闭包的没有返回值，那么我们还可以这样写，
 typealias Anything = () -> Void

 //为接受一个Int类型的参数不返回任何值的闭包类型 定义一个别名：PrintNumber
 typealias PrintNumber = (Int) -> ()

 //为接受两个Int类型的参数并且返回一个Int类型的值的闭包类型 定义一个别名：Add
 typealias Add = (Int, Int) -> (Int)

//为(_ num1: Int, _ num2: Int) -> (Int) 类型的闭包定义别名：Add
 typealias Add = (_ num1: Int, _ num2: Int) -> (Int)
//创建一个 Add 类型的闭包常量：addCloser1
 let addCloser1: Add
//为已经创建好的常量 addCloser1 赋值
 addCloser1 = {
  (_ num1: Int, _ num2: Int) -> (Int) in
  return num1 + num2
 }
//调用闭包并接受返回值
 let result = addCloser1(20, 10)

//创建一个 (_ num1: Int, _ num2: Int) -> (Int) 类型的闭包常量：addCloser1
 let addCloser1: (_ num1: Int, _ num2: Int) -> (Int)
//为已经创建好的常量 addCloser1 赋值
 addCloser1 = {
   (_ num1: Int, _ num2: Int) -> (Int) in
   return num1 + num2
 }
 //调用闭包并接受返回值
 let result = addCloser1(20, 10)

//创建一个 (Int, Int) -> (Int) 类型的闭包常量：addCloser1
 let addCloser1: (Int, Int) -> (Int)
//为已经创建好的常量 addCloser1 赋值
 addCloser1 = {
   (num1, num2) in
   return num1 + num2
 }
//调用闭包并接受返回值
 let result = addCloser1(20, 10)

//创建一个 (Int, Int) -> (Int) 类型的闭包常量：addCloser1 并赋值
 let addCloser1: (Int, Int) -> (Int) = {
   (num1, num2) in
   return num1 + num2
  } 
//调用闭包并接受返回值
 let result = addCloser1(20, 10)

//创建一个 () -> (String) 类型的闭包常量：addCloser1 并赋值
  let addCloser1: () -> (String) = {
   return "这个闭包没有参数，但是有返回值"
   }
 //调用闭包并接受返回值
  let result = addCloser1()

//创建一个 (String, String) -> (String) 类型的闭包常量：addCloser1 并赋值
  let addCloser1: (String, String) -> (String) = {
   return "闭包的返回值是:\($0),\($1)"
   }
 //调用闭包并接受返回值
  let result = addCloser1("Hello", "Swift!")

import UIKit
class SecondViewController: UIViewController {
 //输入文本框
 @IBOutlet weak var textField: UITextField!
 //为创建一个(String) -> () 的可选类型的闭包变量作为控制器的属性
 var closer: ((String) -> ())?
 //返回按钮的点击事件
 @IBAction func backButtonDidClick(_ sender: AnyObject) {
  //首先判断closer闭包是否已经被赋值，如果已经有值，直接调用该闭包，并将输入的文字传进去。
  if closer != nil {
   closer!(textField.text!)
  }
  navigationController?.popViewController(animated: true)
 }
}

import UIKit
class FirstViewController: UIViewController {
 //显示文字的label
 @IBOutlet weak var label: UILabel!
 //重写这个方法
 override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  //拿到跳转的目标控制器
  let secondVC = segue.destination as! SecondViewController
  //为目标控制器的闭包属性赋值
  secondVC.closer = {
   //将闭包的参数(输入的文本内容)显示在label上
   self.label.text = $0
  }
 }
}

//为接受一个Int类型的参数并且返回一个Int类型的值的闭包类型定义一个别名：Number
 typealias Number = (num1: Int) -> (Int)
 //定义一个接收Number类型的参数没有返回值的方法
 func Text(num: Number) {
  //code
 }

//拼接两个字符串和一个整数
 func combine(handle:(String, String) -> (Void), num: Int) {
   handle("hello", "world \(num)")
  }
//方法调用
 combine(handle: { (text, text1) -> (Void) in
   print("\(text) \(text1)")
   }, num: 2016)

 func combine1(num:Int, handle:(String, String)->(Void)) {
   handle("hello", "world \(num)")
 }
 combine1(num: 2016) { (text, text1) -> (Void) in
   print("\(text) \(text1)")
 }

 func combine2(handle:(String, String)->(Void)) {
   handle("hello", "world")
 }
 combine2 { (text, text1) -> (Void) in
   print("\(text) \(text1)")
 }

func request(methodType:RequestMethodType, urlString: String, parameters: [String : AnyObject], completed: @escaping (AnyObject?, NSError?) -> ()) {
  // 1.封装成功的回调
  let successCallBack = { (task : URLSessionDataTask?, result : Any?) -> Void in
   completed(result as AnyObject?, nil)
  }
  // 2.封装失败的回调
  let failureCallBack = { (task : URLSessionDataTask?, error : Error?) -> Void in
   completed(nil, error as NSError?)
  }
  //判断是哪种请求方式
  if methodType == .get {
   get(urlString, parameters: parameters, success: successCallBack, failure: failureCallBack)
  } else {
   post(urlString, parameters: parameters, success: successCallBack, failure: failureCallBack)
  }
 }

import UIKit
class ThirdViewController: UIViewController {
 var callBack: ((String) -> ())?
 override func viewDidLoad() {
  super.viewDidLoad()
  printString { (text) in
   print(text)
   //闭包中捕获了self
   self.view.backgroundColor = UIColor.red
  }
 }
 func printString(callBack:@escaping (String) -> ()) {
  callBack("这个闭包返回一段文字")
  //控制器强引用于着callBack
  self.callBack = callBack
 }
 deinit {
  print("ThirdViewController---释放了")
 }
}

import UIKit
class ThirdViewController: UIViewController {
 var callBack: ((String) -> ())?
 override func viewDidLoad() {
  super.viewDidLoad()
  //将self申明为弱引用类型，打破循环引用
  weak var weakSelf = self
  printString { (text) in
   print(text)
   //闭包中铺捕获了self
   weakSelf?.view.backgroundColor = UIColor.red
  }
 }
 func printString(callBack:@escaping (String) -> ()) {
  callBack("这个闭包返回一段文字")
  //控制器强引用于着callBack
  self.callBack = callBack
 }
 deinit {
  print("ThirdViewController---释放了")
 }
}

import UIKit
class ThirdViewController: UIViewController {
  var callBack: ((String) -> ())?
  override func viewDidLoad() {
    super.viewDidLoad()
    printString {[weak self] (text) in
      print(text)
      self?.view.backgroundColor = UIColor.red
    }
  }
  func printString(callBack:@escaping (String) -> ()) {
    callBack("这个闭包返回一段文字")
    //控制器强引用于着callBack
    self.callBack = callBack
  }
  deinit {
    print("ThirdViewController---释放了")
  }
}

import UIKit
class ThirdViewController: UIViewController {
  var callBack: ((String) -> ())?
  override func viewDidLoad() {
    super.viewDidLoad()
    printString {[unowned self] (text) in
      print(text)
      self?.view.backgroundColor = UIColor.red
    }
  }
  func printString(callBack:@escaping (String) -> ()) {
    callBack("这个闭包返回一段文字")
    //控制器强引用于着callBack
    self.callBack = callBack
  }
  deinit {
    print("ThirdViewController---释放了")
  }
}