几秒钟后关闭UIAlertController？

let alertController = UIAlertController(title: "标题", message: "消息内容", preferredStyle: .alert)
self.present(alertController, animated: true, completion: nil)

DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
    alertController.dismiss(animated: true, completion: nil)
}

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"标题" message:@"消息内容" preferredStyle:UIAlertControllerStyleAlert];
[self presentViewController:alertController animated:YES completion:nil];

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    [alertController dismissViewControllerAnimated:YES completion:nil];
});