在导航页面中获取当前viewController

//获取当前屏幕显示的viewcontroller- (UIViewController *)getCurrentVC{    UIWindow * window = [[UIapplication sharedApplication] keyWindow];    if (window.windowLevel != UIWindowLevelNormal)    {        NSArray *windows = [[UIApplication sharedApplication] windows];        for(UIWindow * tmpWin in windows)        {            if (tmpWin.windowLevel == UIWindowLevelNormal)            {                window = tmpWin;                break;            }        }    }        UIViewController *result = window.rootViewController;    while (result.PResentedViewController) {        result = result.presentedViewController;    }    if ([result isKindOfClass:[RDVTabBarController class]]) {        result = [(RDVTabBarController *)result selectedViewController];    }    if ([result isKindOfClass:[UINavigationController class]]) {        result = [(UINavigationController *)result topViewController];    }    return result;}