c# - GetAsync 请求返回空内容

Question

我想知道为什么当我在 postman 中尝试它有数据返回时它返回空值。这是我的代码。

public async Task<List<HomeViewModel>> GetUserJobs(LoginResult token)
{
    var result = new List<HomeViewModel>();
    string url = "JobHeaders?userName=" + token.userName;
    HttpResponseMessage httpResponse =  await _requestHelper.GetHttpResponse(url, token.access_token);
    result = GetJobResponse(httpResponse);
    return result;
}

获取异步函数

public async Task<HttpResponseMessage> GetHttpResponse(string requestUri, string token)
{
    using (var client = CreateHttpClient(token))
    {
        try
        {
            HttpResponseMessage response = await client.GetAsync(requestUri);

            return response;
        }
        catch (HttpRequestException ex)
        {
            throw new HttpRequestException(ex.Message);
        }
    }
}

添加基地址

private HttpClient CreateHttpClient(string authorization="")
{
    var client = new HttpClient();
    string baseAddress = WebApiBaseAddress;
    if (string.IsNullOrEmpty(baseAddress))
    {
        throw new HttpRequestException("There is no base address specified in the configuration file.");
    }

    client.Timeout = new TimeSpan(0, 5, 59);
    client.BaseAddress = new Uri(baseAddress);
    //client.DefaultRequestHeaders.Accept.Clear();
    client.DefaultRequestHeaders.Add("Authorization", string.Format("bearer {0}", authorization));
    client.DefaultRequestHeaders.Add("Accept", "application/json");
    client.DefaultRequestHeaders.Add("LegacyUse", "true");
    return client;
}

反序列化 JSON

private List<HomeViewModel> GetJobResponse(HttpResponseMessage response)
{
    var result = new List<HomeViewModel>();
    if (response.IsSuccessStatusCode)
    {
        var jsonString = response.Content.ReadAsStringAsync();
        jsonString.Wait();
        if (jsonString.IsCompleted)
        {
            try
            {
                var data = JObject.Parse(jsonString.Result);
                result = JsonConvert.DeserializeObject<List<HomeViewModel>>(data.ToString());
                result.FirstOrDefault().isSuccess = true;
                result.FirstOrDefault().TotalJobs = result.Count();
                result.FirstOrDefault().TotalOpenJobs = result.Where(x => x.JobStatus == "Picked_Up" || x.JobStatus == "Picked Up").ToList().Count();
            }
            catch (Exception ex)
            {
                result.FirstOrDefault().message = ex.Message;
                result.FirstOrDefault().isSuccess = false;
            }
        }
        return result;
    }
    else
    {
        return null;
    }
}

下图是内容为null，状态码为true的httpresponse

这是 Postman 的回复

我也对 web API 做了断点，因为它只在我的本地然后它实际上有数据。

Answer 1

避免混合异步/等待和阻塞调用，如 .Wait() 或 .Result

重构您的代码，使其始终保持异步

private async Task<List<HomeViewModel>> GetJobResponse(HttpResponseMessage response) {
    var result = new List<HomeViewModel>();
    if (response.IsSuccessStatusCode) {
        var jsonString = await response.Content.ReadAsStringAsync();
        try {
            result = JsonConvert.DeserializeObject<List<HomeViewModel>>(jsonString);
            if(result != null && result.Count > 0) {
                result.FirstOrDefault().isSuccess = true;
                result.FirstOrDefault().TotalJobs = result.Count();
                result.FirstOrDefault().TotalOpenJobs = result.Where(x => x.JobStatus == "Picked_Up" || x.JobStatus == "Picked Up").Count();
            }
        } catch (Exception ex) {
            var item = new HomeViewModel {
                message = ex.Message,
                isSuccess = false
            };
            result.Add(item);
        }                
        return result;
    } else {
        return null;
    }
}

并使用

public async Task<List<HomeViewModel>> GetUserJobs(LoginResult token) {
    var result = new List<HomeViewModel>();
    string url = "JobHeaders?userName=" + token.userName;
    HttpResponseMessage httpResponse =  await _requestHelper.GetHttpResponse(url, token.access_token);
    result = await GetJobResponse(httpResponse);
    return result;
}

最后，我建议您回顾一下 HttpClient 应该如何使用。不建议为每个请求创建一个新实例。