异步等待HttpClient.PostAsync调用

Question

我正在尝试将一个调用包装到PostAsync，所以我不必在我的代码库中重新编码调用序列。 我遇到的问题是我从调用中分配的HttpResponseMessage与我的方法调用的消费者不同。 这是代码：

internal class RestHttpClient
{
    public HttpResponseMessage ResponseMessage = new HttpResponseMessage();

    public async void SendRequest(string adaptiveUri, string xmlRequest)
    {
        using (HttpClient httpClient = new HttpClient())
        {
            StringContent httpConent = new StringContent(xmlRequest, Encoding.UTF8);

            try
            {
                ResponseMessage = await httpClient.PostAsync(adaptiveUri, httpConent);
            }
            catch (Exception ex)
            {
                ResponseMessage.StatusCode = HttpStatusCode.InternalServerError;
                ResponseMessage.ReasonPhrase = string.Format("RestHttpClient.SendRequest failed: {0}", ex);
            }
        }
    }
}

我试图调用该方法如下：

RestHttpClient restHttpClient = new RestHttpClient();

restHttpClient.SendRequest(adaptiveUri, xmlRequest);

return restHttpClient.ResponseMessage;

当我进行调用时，ResponseMessage对象始终包含Ok状态，即使这不是从PostAsync调用实际返回的内容。

Answer 1

你看到这个的原因是因为你的方法是async void ，它以“一劳永逸”的方式执行，所以你看到响应消息的实例返回的值，而不是PostAsync的响应。

不要公开单个类HttpResponseMessage字段，如果在同一个实例上并发调用它可能是陈旧的。 相反，每次都返回一个新实例：

public async Task<HttpResponseMessage> SendRequestAsync(string adaptiveUri, string xmlRequest)
{
    using (HttpClient httpClient = new HttpClient())
    {
        StringContent httpConent = new StringContent(xmlRequest, Encoding.UTF8);

        HttpResponseMessage responseMessage = null;
        try
        {
             responseMessage = await httpClient.PostAsync(adaptiveUri, httpConent);
        }
        catch (Exception ex)
        {
            if (responseMessage == null)
            { 
                responseMessage = new HttpResponseMessage();
            }
            responseMessage.StatusCode = HttpStatusCode.InternalServerError;
            responseMessage.ReasonPhrase = string.Format("RestHttpClient.SendRequest failed: {0}", ex);
        }
        return responseMessage;
    }
}

当你调用它时，正确地await它：

return await restHttpClient.SendRequestAsync(adaptiveUri, xmlRequest);