从 MVC 控制器调用包含异步调用的服务的正确模式

Question

我是 TAP 的新手，并且在 C# 的实践中使用 async/await，所以我可能在这里有一些不好的代码味道，所以要温柔。 :-)

我有一个如下所示的服务方法：

public OzCpAddOrUpdateEmailAddressToListOutput AddOrUpdateEmailAddressToList(
    OzCpAddOrUpdateEmailAddressToListInput aParams)
{
    var result = new OzCpAddOrUpdateEmailAddressToListOutput();
    try
    {
        var mailChimManager = new MailChimpManager(aParams.MailChimpApiKey);
        Task<Member> mailChimpResult =
            mailChimManager.Members.AddOrUpdateAsync(
                aParams.Listid, 
                new Member                                                                                                     
                {
                    EmailAddress = aParams.EmailAddress
                });

        //Poll async task until it completes. 
        //Give it at most 8 seconds to do what it needs to do
        var outOfTime = DateTime.Now.AddSeconds(8);
        while (!mailChimpResult.IsCompleted)
        {
            if (DateTime.Now > outOfTime)
            {
                throw new Exception("Timed out waiting for MailChimp API.");
            }
        }

        //Should there have been a problem with the call then we raise an exception
        if (mailChimpResult.IsFaulted)
        {
            throw new Exception(
                mailChimpResult.Exception?.Message ?? 
                "Unknown mail chimp library error.", 
                mailChimpResult.Exception);
        }
        else
        {
            //Call to api returned without failing but unless we have 
            //the email address subscribed we have an issue
            if (mailChimpResult.Result.Status != Status.Subscribed)
            {
                throw new Exception(
                    $"There was a problem subscribing the email address
                    {aParams.EmailAddress} to the mailchimp list id 
                    {aParams.Listid}");
            }
        }
    }
    catch (Exception ex)
    {
        result.ResultErrors.AddFatalError(PlatformErrors.UNKNOWN, ex.Message);
    }
    return result;
}

但是当我从 MVC 控制器 调用时，动作 mailChimpResult.IsCompleted 总是返回 false，最终我遇到了超时。

我意识到这是因为我没有按照 HttpClient IsComplete always return false 链接异步调用，并且由于线程不同，这种行为是“预期的”。

但是，我希望我的服务方法隐藏它正在做的事情的 async 性质的复杂性，并且只在我的操作方法中执行看似同步调用的操作：

 var mailChimpResult =
    _PlatformMailChimpService.AddOrUpdateEmailAddressToList(
        new OzCpAddOrUpdateEmailAddressToListInput                                                                                                                                            
        {
            EmailAddress = aFormCollection["aEmailAddress"],                                                                                                                                           
            Listid = ApplicationSettings.Newsletter.MailChimpListId.Value,                                                                                                                                          
            MailChimpApiKey = ApplicationSettings.Newsletter.MailChimpApiKey.Value
        });

 if (mailChimpResult.Result == true)
 {
    //So something
 }

Answer 1

理想情况下，您应该避免 Task 和 Task<T> 对象的 .Result 和 .IsFaulted 属性，这是代码气味的第一名。当您使用这些对象时，您应该在整个堆栈中使用async 和await。考虑以这种方式编写您的服务：

public async Task<OzCpAddOrUpdateEmailAddressToListOutput> 
    AddOrUpdateEmailAddressToList(
        OzCpAddOrUpdateEmailAddressToListInput aParams)
{
    var result = new OzCpAddOrUpdateEmailAddressToListOutput();
    try
    {
        var mailChimManager = new MailChimpManager(aParams.MailChimpApiKey);
        Member mailChimpResult =
            await mailChimManager.Members.AddOrUpdateAsync(
                aParams.Listid, 
                new Member                                                                                                     
                {
                    EmailAddress = aParams.EmailAddress
                });
    }
    catch (Exception ex)
    {
        result.ResultErrors.AddFatalError(PlatformErrors.UNKNOWN, ex.Message);
    }
    return result;
}

请注意，我能够删除所有不必要的轮询和属性检查。我们将方法标记为Task<OzCpAddOrUpdateEmailAddressToListOutput> 返回并用async 关键字装饰它。这允许我们在方法体中使用await 关键字。我们await.AddOrUpdateAsync 产生Member。

对服务的消费调用看起来很相似，遵循 async 和 await 关键字的相同范例，带有 Task 或 Task<T> 返回类型：

var mailChimpResult =
    await _PlatformMailChimpService.AddOrUpdateEmailAddressToList(
        new OzCpAddOrUpdateEmailAddressToListInput                                                                                                                                            
        {
            EmailAddress = aFormCollection["aEmailAddress"],                                                                                                                                           
            Listid = ApplicationSettings.Newsletter.MailChimpListId.Value,                                                                                                                                          
            MailChimpApiKey = ApplicationSettings.Newsletter.MailChimpApiKey.Value
        });

 if (mailChimpResult.Result == true)
 {
    //So something
 }

最好的做法是在方法后面加上“Async”这个词，表示它是异步的，即； AddOrUpdateEmailAddressToListAsync.