获取当前最上层vc，获取当前活动的navigationview

/**
 *  获取当前最上层VC
 *
 *  @return <#return value description#>
*/
- (UIViewController *)getTopViewController {
    UIViewController *result = nil;

    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;
            }
        }
    }

    UIView *frontView = [[window subviews] objectAtIndex:0];
    id nextResponder = [frontView nextResponder];

    if ([nextResponder isKindOfClass:[UIViewController class]]) {
        result = nextResponder;
    } else {
        result = window.rootViewController;
    }
    return result;
} 

/**
 *  获取当前活动的navigationcontroller
 *
 *  @return <#return value description#>
 */
- (UINavigationController *)navigationViewController {
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    if ([window.rootViewController isKindOfClass:[UINavigationController class]]) {
        return (UINavigationController *)window.rootViewController;
    } else if ([window.rootViewController isKindOfClass:[UITabBarController class]]) {
        UIViewController *selectVc = [((UITabBarController *)window.rootViewController)selectedViewController];
        if ([selectVc isKindOfClass:[UINavigationController class]]) {
            return (UINavigationController *)selectVc;
        }
    }
    return nil;
}