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
}

}