final class FindHelper {

static let share = FindHelper()

var currentViewCotroller: UIViewController? {
    
    var result: UIViewController? = nil
    var window: UIWindow
    
    guard let _window = UIApplication.shared.keyWindow else {
        return result
    }
    window = _window
    
    if window.windowLevel != UIWindow.Level.normal {
        guard let _tmpWin =  UIApplication.shared.windows
            .filter({ $0.windowLevel == UIWindow.Level.normal })
            .first else {
                return result
        }
        window = _tmpWin
    }
    
    var nextResponder: UIResponder? = nil
    let appRootVC = window.rootViewController
    
    // 如果是present上來(lái)的appRootVC.presentedViewController 不為nil
    if let presentedVC = appRootVC?.presentedViewController {
        nextResponder = presentedVC
    } else {
        let frontView = window.subviews[0]
        nextResponder = frontView.next
    }
    
    if let tabbar = nextResponder as? UITabBarController {
        if let nav = tabbar.viewControllers?[tabbar.selectedIndex] as? UINavigationController {
            result = nav.children.last
        }
    } else if let nav = nextResponder as? UINavigationController {
        result = nav.children.last
    } else {
        result = nextResponder as? UIViewController
    }
    
    return result
}
}