Swift利用闭包（closure）来实现传值-->前后两个控制器的反向传值

利用了大约一个多小时来搞明白OC中Blocks反向传值和Swift中Closure反向传值的差别，下面直接贴上代码：

一、第一个界面

//  Created by 秦志伟 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:"下一页",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)
        //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)
        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.
    }


    /*
    // #pragma mark - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
        // Get the new view controller using [segue destinationViewController].
        // Pass the selected object to the new view controller.
    }
    */

}

二、第二个界面

//  Created by 秦志伟 on 14-6-13.
import UIKit
//类似于OC中的typedef
typealias sendValueClosure=(string:String)->Void
class ZWSecondViewController: UIViewController {
    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
    }

    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("点击我" ,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{
            //闭包隐式调用someFunctionThatTakesAClosure函数：回调。
            myClosure!(string: "好好哦\(i)")
        }
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    /*
    // #pragma mark - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
        // Get the new view controller using [segue destinationViewController].
        // Pass the selected object to the new view controller.
    }
    */

}

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