//獲取到展示在屏幕前的這個控制器

• (UIViewController *)topViewController {
  UIViewController *resultVC;
  resultVC = [self _topViewController:[[UIApplication sharedApplication].keyWindow rootViewController]];
  while (resultVC.presentedViewController) {
  resultVC = [self _topViewController:resultVC.presentedViewController];
  }
  return resultVC;
  }

• (UIViewController *)_topViewController:(UIViewController *)vc {
  if ([vc isKindOfClass:[UINavigationController class]]) {
  return [self _topViewController:[(UINavigationController *)vc topViewController]];
  } else if ([vc isKindOfClass:[UITabBarController class]]) {
  return [self _topViewController:[(UITabBarController *)vc selectedViewController]];
  } else {
  return vc;
  }
  return nil;
  }

//調用
[[self topViewController].navigationController pushViewController:businessVC animated:YES];