if let nav = navigationController, let pan = nav.interactivePopGestureRecognizer {
            if !isLocalNavigationRootViewController { 
                scrollView.panGestureRecognizer.require(toFail: pan)
            }
        }

// 判断当前控制器是不是栈中的第一个控制器
    private var isLocalNavigationRootViewController:Bool {
        guard let nav = self.navigationController,let root = nav.viewControllers.first else {
            return false
        }
        
        var vc:UIViewController? = self
        while (vc != nil) {
            if vc == nav {
                return false
            } else if vc == root {
                return true
            }
            vc = vc?.parent
        }
        return false
    }