官网文档 protocol
该协议可以通过一个类，结构或枚举 定义这些需要的方法

首先我们创建一个UIView 来实现AlertView 的载体
命名为 SwiftCustomAlertView.swift

首先我们假设AlertView 有两个按钮，确定和取消
我们要实现这两个按钮的协议来通知控制器我们点击了哪个按钮。如下

下面就具体如何实现AlertView 界面 写得都非常简单一看就明白，我就不具体说明了，具体思路掌握了，就可以任意自定义控件了

@objc protocol SwiftCustomAlertViewDelegate : NSObjectProtocol{

    optional func  selectOkButtonalertView()

    optional func  selecttCancelButtonAlertView()

}

optional 操作符来指定协议可以不实现
继承 NSObjectProtocol 可以用来后面调用respondsToSelector 方法检测是否实现了该delegate
如果需要传值可以在方法里添class

SwiftCustomAlertView: UIView {




    private let defaultWidth        = 280.0  //默认Alert宽度
    private let defaultHeight       = 146.0  //默认Alert高度
    private let defaultCornerRadius = 5.0    //默认Alert 圆角度数

    private var viewY:Double!
    private var viewWidth: Double!
    private var viewHeight: Double!

    private var cancelButtonTitle: String?
    private var oKButtonTitle: String?

    private var cancelButton: UIButton?
    private var oKButton: UIButton?

    private var title: String?
    private var message: String?

    private var titleLabel: UILabel!
    private var messageLabel: UILabel!

    var cornerRadius: Double!

    weak var delegate: SwiftCustomAlertViewDelegate? // delegate



    //初始化
    init(title: String?, message: String?, delegate: SwiftCustomAlertViewDelegate?) {

        super.init(frame: CGRect(x: 0, y: 0, width: defaultWidth, height: defaultHeight))

          setup(title, message: message,delegate: delegate)
      }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    //设置相关数据
    private func setup(title: String?, message: String?,delegate: SwiftCustomAlertViewDelegate?) {

        self.title = title
        self.message = message
        self.delegate = delegate
        self.setUpDefaultValue()
        self.setUpElements()
      }

    //默认参数
    private func setUpDefaultValue() {

        clipsToBounds = true
        cancelButtonTitle = "取消"
        oKButtonTitle = "确定"
        viewWidth = defaultWidth
        viewHeight = defaultHeight
        cornerRadius = defaultCornerRadius
        layer.cornerRadius = CGFloat(cornerRadius)
        self.backgroundColor = UIColor.redColor()
    }

    //设置相关ui
    private func setUpElements() {
        titleLabel = UILabel(frame: CGRectZero)
        messageLabel = UILabel(frame: CGRectZero)

        if title != nil {
            titleLabel.text = title
            titleLabel.numberOfLines = 0
            titleLabel.lineBreakMode = NSLineBreakMode.ByWordWrapping
            titleLabel.textColor = UIColor.blackColor()
            titleLabel.font = UIFont.boldSystemFontOfSize(17)
            titleLabel.textAlignment = NSTextAlignment.Center
            titleLabel.backgroundColor = UIColor.clearColor()
            addSubview(titleLabel)
        }
        if message != nil {
            messageLabel.text = message
            messageLabel.numberOfLines = 0
            messageLabel.lineBreakMode = NSLineBreakMode.ByWordWrapping
            messageLabel.textColor = UIColor.blackColor()
            messageLabel.font = UIFont.systemFontOfSize(13)
            messageLabel.textAlignment = NSTextAlignment.Center
            messageLabel.backgroundColor = UIColor.clearColor()
            addSubview(messageLabel)
        }


        if let cancelTitle = cancelButtonTitle {

            cancelButton = UIButton(type: UIButtonType.Custom)

            cancelButton!.setTitle(cancelTitle, forState: UIControlState.Normal)

            cancelButton!.backgroundColor = UIColor.blueColor()

            cancelButton!.setTitleColor(UIColor.blackColor(), forState: UIControlState.Normal)
            cancelButton!.titleLabel?.font = UIFont.boldSystemFontOfSize(17)

            cancelButton?.tag = 9

            addSubview(cancelButton!)
        }

        if let okTitle = oKButtonTitle {

            oKButton = UIButton(type: UIButtonType.Custom)

            oKButton!.setTitle(okTitle, forState: UIControlState.Normal)

            oKButton!.backgroundColor = UIColor.yellowColor()

            oKButton!.setTitleColor(UIColor.blackColor(), forState: UIControlState.Normal)
            oKButton!.titleLabel?.font = UIFont.boldSystemFontOfSize(17)

            oKButton?.tag = 10

            addSubview(oKButton!)
        }


    }

    private func layoutFrameshowing() {

         cancelButton!.addTarget(self, action: Selector("cancelButtonClicked:"), forControlEvents: UIControlEvents.TouchUpInside)

         cancelButton!.frame = CGRect(x: viewWidth/2, y: viewHeight-40, width: viewWidth/2, height: 40)

        oKButton!.addTarget(self, action: Selector("okButtonClicked:"), forControlEvents: UIControlEvents.TouchUpInside)

        oKButton!.frame = CGRect(x:0, y: viewHeight-40, width: viewWidth/2, height: 40)

        if title != nil {

            titleLabel.frame = CGRect(x: 10, y: 5, width: viewWidth - 20, height: 20)

        }
        if message != nil {
            messageLabel.frame = CGRect(x: 10, y: 0, width: viewWidth - 20, height: 0)
            labelHeightToFit(messageLabel)
        }

        if message != nil {

            messageLabel.center = CGPoint(x: viewWidth/2, y: 5 + Double(titleLabel.frame.size.height) + 20 + Double(messageLabel.frame.size.height)/2)
        }


    }
    private func labelHeightToFit(label: UILabel) {

        let maxWidth = label.frame.size.width - 20
        let maxHeight : CGFloat = 500
        let rect = label.attributedText?.boundingRectWithSize(CGSizeMake(maxWidth, maxHeight),
            options: .UsesLineFragmentOrigin, context: nil)
        var frame = label.frame
        frame.size.height = rect!.size.height
        label.frame = frame
    }


    func cancelButtonClicked(button: UIButton) {


        UIView.animateWithDuration(0.5, animations: { () -> Void in

            self.center = CGPoint(x: -self.viewWidth , y:self.viewY + self.viewHeight/2)

            }) { (Bool) -> Void in

            self.removeFromSuperview()
        }

        if delegate?.respondsToSelector(Selector("selecttCancelButtonAlertView")) == true {

           print("cancelDelegate")

            delegate?.selecttCancelButtonAlertView!()
        }


    }
    func okButtonClicked(button: UIButton) {

        UIView.animateWithDuration(0.5, animations: { () -> Void in

             self.center = CGPoint(x:Double(UIScreen .mainScreen().bounds.size.width)+self.viewWidth , y:self.viewY + self.viewHeight/2)

            }) { (Bool) -> Void in

                self.removeFromSuperview()
        }

        if delegate?.respondsToSelector(Selector("selectOkButtonalertView")) == true {

            delegate?.selectOkButtonalertView!()
        }

    }

    func show() {

        if let window: UIWindow = UIApplication.sharedApplication().keyWindow {
            show(window)
        }
    }

    func show(view: UIView) {

        layoutFrameshowing()

        self.viewY = (Double(view.frame.size.height) - viewHeight)/2

        self.frame = CGRect(x: (Double(view.frame.size.width) - viewWidth)/2, y: viewY, width: viewWidth, height: viewHeight)

        view.addSubview(self)

        view.bringSubviewToFront(self)

        self.alpha = 0.3
        UIView.animateWithDuration(0.2, delay: 0.0, options: .CurveEaseOut, animations: {

            self.alpha = 1;
            self.transform =  CGAffineTransformMakeScale(0.8, 0.8)
            }, completion: { finished in

                UIView.animateWithDuration(0.2, animations: {() -> Void in

                    self.transform = CGAffineTransformMakeScale(1.2, 1.2)

                    }) { (Bool) -> Void in

                        UIView.animateWithDuration(0.1, animations: { () -> Void in

                            self.transform = CGAffineTransformMakeScale(1, 1)
                        })
                }
        })


    }

}

在调用的地方

      let alertView = SwiftCustomAlertView(title:"swift", message:"custom swift alert", delegate: self)
      alertView .show();

和实现delegate方法

  func selectOkButtonalertView() {


    }

  func selecttCancelButtonAlertView() {


    }