继承UIControl

class Slider: UIControl {

    let trackView = UIView()
    
    var minValue: CGFloat = 0
    var maxValue: CGFloat = 1
    
    var currentValue: CGFloat = 0.5 {
        didSet {
//            self.sendActionsForControlEvents(.ValueChanged)
            
            self.setNeedsLayout()
        }
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        self.addSubview(trackView)
        
        self.backgroundColor = UIColor.cyanColor()
        trackView.backgroundColor = UIColor.redColor()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        
        self.addSubview(trackView)
        
        self.backgroundColor = UIColor.cyanColor()
        trackView.backgroundColor = UIColor.redColor()
    }
    
    func moveTrack(touches: NSSet) {
        let touch = touches.anyObject() as! UITouch
        
        let location = touch.locationInView(self)
        currentValue = (location.x / self.frame.size.width) * (maxValue - minValue) + minValue
    }
    
    //开始触摸
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
//        print("begin")
        
        moveTrack(touches)
    }
    
    //移动
    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
//        print("continue")
        
        moveTrack(touches)
    }
    
    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
//        print("end")
        
        //触发事件
        self.sendActionsForControlEvents(.ValueChanged)
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        let width = (currentValue - minValue) * self.frame.size.width / (maxValue - minValue)
        let rect = CGRect(x: 0, y: 0, width: width, height: self.frame.size.height)
        trackView.frame = rect
    }
}


{
   let slider = ProtocolSlider(frame: CGRect(x: 100, y: 100, width: 200, height: 50))
   slider.addTarget(self, action: #selector(didChange(_:)), forControlEvents: .ValueChanged)
   self.view.addSubview(slider)
}

协议和闭包方法封装

//协议的优点：明确
//协议的缺点：复杂，步骤太多
//如果有optional方法，必须使用@objc
@objc protocol ProtocolSliderDelegate {
    optional func didChange(slider: ProtocolSlider)
}

class ProtocolSlider: UIView {

    let trackView = UIView()
    
    //用于关联两个对象(控件与需要获取事件的对象)
    var delegate: ProtocolSliderDelegate!
    
    var didChange: ((ProtocolSlider) -> Void)!
    
    var minValue: CGFloat = 0
    var maxValue: CGFloat = 1
    
    var currentValue: CGFloat = 0.5 {
        didSet {
            //            self.sendActionsForControlEvents(.ValueChanged)
            
            self.setNeedsLayout()
        }
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        self.addSubview(trackView)
        
        self.backgroundColor = UIColor.cyanColor()
        trackView.backgroundColor = UIColor.redColor()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        
        self.addSubview(trackView)
        
        self.backgroundColor = UIColor.cyanColor()
        trackView.backgroundColor = UIColor.redColor()
    }
    
    func moveTrack(touches: NSSet) {
        let touch = touches.anyObject() as! UITouch
        
        let location = touch.locationInView(self)
        currentValue = (location.x / self.frame.size.width) * (maxValue - minValue) + minValue
    }
    
    //开始触摸
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        //        print("begin")
        
        moveTrack(touches)
    }
    
    //移动
    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        //        print("continue")
        
        moveTrack(touches)
    }
    
    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        //        print("end")
        
        //触发事件
//        self.sendActionsForControlEvents(.ValueChanged)
        //1. 如果使用协议，需要确保delegate是否为空
        //2. 如果方法为optional，需要确保方法是否实现
//        if delegate != nil {
//            if delegate.didChange != nil {
//                delegate.didChange!(self)
//            }
//        }
        
        if didChange != nil {
            didChange(self)
        }
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        let width = (currentValue - minValue) * self.frame.size.width / (maxValue - minValue)
        let rect = CGRect(x: 0, y: 0, width: width, height: self.frame.size.height)
        trackView.frame = rect
    }

}


{
        let slider = ProtocolSlider(frame: CGRect(x: 100, y: 100, width: 200, height: 50))
//        slider.delegate = self
        
//        slider.didChange = {
//            sender in
//            print(sender.currentValue)
//        }
        
        //函数：特殊闭包
        //闭包：匿名函数
        slider.didChange = didChange
        slider.didChange = {
            print($0.currentValue)
        }
        self.view.addSubview(slider)
    }
    
    func didChange(sender: ProtocolSlider) {
        print(sender.currentValue)
    }