原文如下：
Swift利用閉包（closure）來實現傳值-->前後兩個控制器的反向傳值
利用了大約一個多小時來搞明白OC中Blocks反向傳值和Swift中Closure反向傳值的差別，下面直接貼上代碼：
一、第一個界面
// Created by 秦志偉 on 14-6-13.
import UIKit
class ZWRootViewController: UIViewController {
init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
// Custom initialization
}
var myLabel:UILabel?
override func viewDidLoad() {
super.viewDidLoad()
var item = UIBarButtonItem(title:"下一頁",style:UIBarButtonItemStyle.Plain,target:self,action:"nextBtnClicked")
self.navigationItem.rightBarButtonItem = item
myLabel = UILabel(frame:CGRectMake(0,100,320,50))
myLabel!.text = "Closure"
myLabel!.textAlignment = NSTextAlignment.Center
self.view.addSubview(myLabel!)
// Do any additional setup after loading the view.
}
func someFunctionThatTakesAClosure(string:String) -> Void {
// function body goes here
myLabel!.text = string
}
func nextBtnClicked(){
let second = ZWSecondViewController(nibName:nil,bundle:nil)
//將當前someFunctionThatTakesAClosure函數指針傳到第二個界面，第二個界面的閉包拿到該函數指針後會進行回調該函數
second.initWithClosure(someFunctionThatTakesAClosure)
self.navigationController.pushViewController(second,animated:true)
}
override func viewWillDisappear(animated: Bool){
myLabel!.hidden = true
}
override func viewWillAppear(animated: Bool){
myLabel!.hidden = false
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
二、第二個界面
// Created by 秦志偉 on 14-6-13.
import UIKit
//類似於OC中的typedef
typealias sendValueClosure=(string:String)->Void
class ZWSecondViewController: UIViewController {
var i:Int?
//聲明一個閉包
var myClosure:sendValueClosure?
//下面這個方法需要傳入上個界面的someFunctionThatTakesAClosure函數指針
func initWithClosure(closure:sendValueClosure?){
//將函數指針賦值給myClosure閉包，該閉包中涵蓋了someFunctionThatTakesAClosure函數中的局部變量等的引用
myClosure = closure
}
init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
// Custom initialization
}
override func viewDidLoad() {
super.viewDidLoad()
i = 0
var btn = UIButton.buttonWithType(UIButtonType.System) as?UIButton
btn!.frame = CGRectMake(0,100,320,50)
btn!.setTitle("點擊我" ,forState:UIControlState.Normal)
btn!.addTarget(self,action:"action", forControlEvents:UIControlEvents.TouchUpInside)
self.view.addSubview(btn)
// Do any additional setup after loading the view.
}
func action(){
i = i!+1
//判空
if myClosure{
//閉包隱式調用someFunctionThatTakesAClosure函數：回調。
myClosure!(string: "好好哦\(i)")
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}