swift协议代理

ViewController.swift

import UIKit
class ViewController: UIViewController,ViewController2Delegate {
    var label:UILabel?
    override func viewDidLoad() {
        super.viewDidLoad()
        label = UILabel.init(frame: CGRect(x: 20,y: 80,width: 280,height: 30))
        label?.text = "我是界面一"
        label?.textColor = UIColor.blackColor()
        self.view.addSubview(label!)
    }
    override func touchesBegan(touches: Set<</span>UITouch>, withEvent event: UIEvent?) {
        let vc2 = ViewController2.init()
        vc2.delegate = self
        self.presentViewController(vc2, animated: true, completion: nil)
    }
    //MARK-协议代理实现部分
    func click(str:NSString)->(){
        label?.text = str as String
    }
}

ViewController2.swift

import UIKit
@objc protocol  ViewController2Delegate{
     //optional表示可选方法，若不写，ViewController里就必须实现不然会报错
    optional func click(str:NSString)->()
}
class ViewController2: UIViewController {

    var delegate:ViewController2Delegate?
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = UIColor.redColor()
    }
    override func touchesBegan(touches: Set<</span>UITouch>, withEvent event: UIEvent?) {
        self.delegate?.click!("界面二被点击了,界面一显示下")
        self.dismissViewControllerAnimated(true, completion: nil)
    }
}