view.addSubview(leftMenuVC.view)
   view.addSubview(mainVC.view)

   addChildViewController(leftMenuVC)
   addChildViewController(mainVC)

//MARK: - 打开左侧菜单
  func openLeftMenu() {

    UIView.animate(withDuration: 0.25, delay: 0, options: UIViewAnimationOptions.curveLinear, animations: {

      self.leftVC?.view.transform = CGAffineTransform.identity
      self.mainVC?.view.transform = CGAffineTransform(translationX: self.maxWidth, y: 0)


    }, completion: {

      (finish: Bool) -> () in

      self.mainVC?.view.addSubview(self.coverBtn)

    })

  }

  //MARK: - 关闭左侧菜单
  func closeLeftMenu() {

    UIView.animate(withDuration: 0.25, delay: 0, options: UIViewAnimationOptions.curveLinear, animations: {

      self.leftVC?.view.transform = CGAffineTransform(translationX: -self.maxWidth, y: 0)
      self.mainVC?.view.transform = CGAffineTransform.identity


    }, completion: {

      (finish: Bool) -> () in

      self.coverBtn.removeFromSuperview()

    })


  }

for childViewController in (mainVC?.childViewControllers)! {

     addScreenEdgePanGestureRecognizerToView(view: childViewController.view)

   }

//MARK: - 添加屏幕边缘手势
  private func addScreenEdgePanGestureRecognizerToView(view: UIView) {

    let pan = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(edgPanGesture(_:)))
    pan.edges = UIRectEdge.left
    view.addGestureRecognizer(pan)

  }

//MARK: - 屏幕左边缘手势
  func edgPanGesture(_ pan: UIScreenEdgePanGestureRecognizer) {

    let offsetX = pan.translation(in: pan.view).x

    if pan.state == UIGestureRecognizerState.changed && offsetX <= maxWidth {

      mainVC?.view.transform = CGAffineTransform(translationX: max(offsetX, 0), y: 0)
      leftVC?.view.transform = CGAffineTransform(translationX: -maxWidth + offsetX, y: 0)

    } else if pan.state == UIGestureRecognizerState.ended || pan.state == UIGestureRecognizerState.cancelled || pan.state == UIGestureRecognizerState.failed {

      if offsetX > screenW * 0.5 {

        openLeftMenu()

      } else {

        closeLeftMenu()
      }

    }

  }

//MARK: - 遮盖按钮手势
  func panCloseLeftMenu(_ pan: UIPanGestureRecognizer) {

    let offsetX = pan.translation(in: pan.view).x
    if offsetX > 0 {return}

    if pan.state == UIGestureRecognizerState.changed && offsetX >= -maxWidth {

      let distace = maxWidth + offsetX

      mainVC?.view.transform = CGAffineTransform(translationX: distace, y: 0)
      leftVC?.view.transform = CGAffineTransform(translationX: offsetX, y: 0)

    } else if pan.state == UIGestureRecognizerState.ended || pan.state == UIGestureRecognizerState.cancelled || pan.state == UIGestureRecognizerState.failed {

      if offsetX > screenW * 0.5 {

        openLeftMenu()

      } else {

        closeLeftMenu()
      }

    }

  }

@IBAction func showAlert(_ sender: UIBarButtonItem) {

    let popVC = PopViewController()
    popVC.modalPresentationStyle = UIModalPresentationStyle.popover
    popVC.popoverPresentationController?.barButtonItem = sender
    popVC.popoverPresentationController?.delegate = self
    //可控制三角颜色
    popVC.popoverPresentationController?.backgroundColor = UIColor.white
    present(popVC, animated: true, completion: nil)

  }


  func adaptivePresentationStyle(for controller: UIPresentationController) -> UIModalPresentationStyle {
    return UIModalPresentationStyle.none
  }

  func popoverPresentationControllerShouldDismissPopover(_ popoverPresentationController: UIPopoverPresentationController) -> Bool {
    return true
  }