ios swift 左侧抽屉简单实现

var leftView: UIView?    var minX: CGFloat?    var midX: CGFloat?    var maxX:CGFloat?    /*     抽屉     */    func drawerView(){        self.view.isMultipleTouchEnabled = true        self.view.isUserInteractionEnabled = true        self.view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(self.pan(_:))))        let make = CGRect(x: -UIScreen.main.bounds.width*3/5, y: 0, width: UIScreen.main.bounds.width*3/5, height: UIScreen.main.bounds.height)        leftView = UIView(frame: make)        leftView?.backgroundColor = UIColor.brown        self.view.addSubview(leftView!)        minX = leftView?.center.x        maxX = minX! + make.width        midX = (maxX!-minX!)/2 + minX!        }func pan(_ pan: UIPanGestureRecognizer){                switch pan.state{                case UIGestureRecognizerState.began:            PRint("----began----")                    case UIGestureRecognizerState.changed:            print("----Changed----")            let tran = pan.translation(in: self.view)            let newC = (leftView?.center.x)! + tran.x            if newC >= minX && newC <= maxX{                leftView?.center = CGPoint(x: newC, y: (leftView?.center.y)!)            }            pan.setTranslation(CGPoint.zero, in: self.view)        case UIGestureRecognizerState.ended:                UIView.animate(withDuration: 0.2, animations: { () -> Void in                if self.leftView!.center.x > self.minX && self.leftView!.center.x < self.midX{                    self.leftView!.center = CGPoint(x: self.minX!, y: self.leftView!.center.y)                }else if self.leftView!.center.x >= self.midX && self.leftView!.center.x < self.maxX{                    self.leftView!.center = CGPoint(x: self.maxX!, y: self.leftView!.center.y)                }                }, completion: { (finish) -> Void in                                })                    default: break        }        }