ios 获取当前处于活动的viewController

#pragma mark - 获取当前活动的viewcontroller- (UIViewController*)topViewController {    return [self topViewControllerWithRootViewController:[UIApplication sharedApplication].keyWindow.rootViewController];}- (UIViewController*)topViewControllerWithRootViewController:(UIViewController*)rootViewController {    if ([rootViewController isKindOfClass:[UITabBarController class]]) {        UITabBarController* tabBarController = (UITabBarController*)rootViewController;        return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];    } else if ([rootViewController isKindOfClass:[UINavigationController class]]) {        UINavigationController* navigationController = (UINavigationController*)rootViewController;        return [self topViewControllerWithRootViewController:navigationController.visibleViewController];    } else if (rootViewController.presentedViewController) {        UIViewController* presentedViewController = rootViewController.presentedViewController;        return [self topViewControllerWithRootViewController:presentedViewController];    } else {        return rootViewController;    }}