Swift：闭包(Closures)

标签：闭包   swift   closures   

一、 基本概念 

闭包（Closures）是自包含的功能代码块，可以在代码中使用或者用来作为参数传值。 在Swift中的闭包与C、OC中的blocks和其它编程语言（如C#）中的lambda, javascript中的函数嵌套等类似。 闭包可以捕获和存储上下文中定义的的任何常量和变量的引用。这就是所谓的变量和变量的自封闭， 因此闭包还会处理所有捕获的引用的内存管理。 全局函数和嵌套函数其实就是特殊的闭包。 闭包的形式有： 

(4)提供了尾随闭包语法(Trailing closure syntax) 

var names = ["Swift", "Arial", "Soga", "Donary"]

func backwards(firstString: String, secondString: String) -> Bool {  
   return firstString > secondString // 降序排序  
 }

sort(&names, backwards)

这种方式的使用相当于回调backward方法。

sort(&names, { (firstString: String, secondString: String) -> Bool in  
    return firstString > secondString  
    }) 

sort(&names, { (firstString: String, secondString: String) -> Bool in return firstString > secondString})

sort(&names, { firstString, secondString in return firstString > secondString}) 

sort(&names, { firstString, secondString in firstString > secondString})

sort(&names, { $0 > $1 })  

sort(&names, >)

sort(&names, { (firstString: String, secondString: String) -> Bool in  
    return firstString > secondString  
    }) 

sort(&names){
    (firstString, secondString) -> Bool in
    return firstString > secondString
}

var numbers = [1,2,3]
let strings = numbers.map({
    (var number) -> String in
    var output = ""
    while number > 0 {
        output = String(number % 10) + output
        number /= 10
    }
    return output
})

var numbers = [1,2,3]
let strings = numbers.map(){
    (var number) -> String in
    var output = ""
    while number > 0 {
        output = String(number % 10) + output
        number /= 10
    }
    return output
}

var numbers = [1,2,3]
let strings = numbers.map{
    (var number) -> String in
    var output = ""
    while number > 0 {
        output = String(number % 10) + output
        number /= 10
    }
    return output
}

func increment(#amount: Int) -> (() -> Int) {  
  var total = 0  
  func incrementAmount() -> Int {  
    total += amount // total是外部函数体内的变量，这里是可以捕获到的  
    return total  
  }  
  return incrementAmount // 返回的是一个嵌套函数（闭包）  
}

let incrementByTen = increment(amount: 10)   
incrementByTen() // return 10,incrementByTen是一个闭包  
// 这里是没有改变对increment的引用，所以会保存之前的值  
incrementByTen() // return 20     
incrementByTen() // return 30     
  
let incrementByOne = increment(amount: 1)  
incrementByOne() // return 1  
incrementByOne() // return 2      
incrementByTen() // return 40   
incrementByOne() // return 3  

__weak typeof(self) wSelf = self;

class HTMLElement {
    var name: String
    var text: String?
    
    init(name: String, text: String?) {
        self.name = name
        self.text = text
    }
    
    lazy var asHtml: () -> String = {
        [unowned self] in
        if let text = self.text {
            return "<\(self.name)>\(self.text)</\(self.name)>"
        } else {
            return "<\(self.name)>"
        }
    }
}


var html = HTMLElement(name: "Node", text: "Jack")
html.asHtml()

上面的代码中，self对asHtml这个闭包属性有强引用，而asHtml内部又有对self的强引用，所以我们可以使用[unowned self] 将self “弱化”。从而解除了循环引用。

class TestView: UIView {


    private weak var textField1: UITextField!
    
    var testClosure: ((str1: String) -> Void)?
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        var size = UIScreen.mainScreen().bounds.size
        self.frame = CGRectMake(0, 0, size.width, kViewHeight)
        self.backgroundColor = UIColor.grayColor()
        
        var textField1 = UITextField(frame: CGRectMake(10, 30, 150, 30))
        textField1.backgroundColor = UIColor.whiteColor()
        self.addSubview(textField1)
        self.textField1 = textField1
        
        var btn = UIButton(frame: CGRectMake(300, 30, 50, 30))
        btn.setTitle("GO", forState: UIControlState.Normal)
        btn.addTarget(self, action: "showResult", forControlEvents: UIControlEvents.TouchDown)
        self.addSubview(btn)
    }
    
    func showResult() {
        self.testClosure?(str1: self.textField1.text)
    }
    
    required init(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

var testClosure: ((str1: String) -> Void)?

self.testClosure?(str1: self.textField1.text)

class ViewController: UIViewController {
    
    @IBOutlet weak var testLabel: UILabel!


    override func viewDidLoad() {
        super.viewDidLoad()
        
        var tab = TestView()
        tab.testClosure = {
            [unowned self] // 去除循环引用
            (str1: String) -> Void in
            self.testLabel.text = "First Record:\(str1)"
        }
        self.view.addSubview(tab)
    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Swift：闭包(Closures)

标签：闭包   swift   closures   

原文地址：http://blog.csdn.net/sinat_27706697/article/details/47441573