HttpClient 如何在一个地方捕获每个响应

Question

我正在开发与 Web Api 2 Api 连接的 Xamarin.Forms 应用程序，所有请求和响应都与 HttClient 一起工作。这是我的代码：

我所有请求的类和 HttpClient 的定义

  public class DataStore : IDataStore<object>
    {
        HttpClient client;

        public DataStore()
        {
            client = new HttpClient()
            {
                BaseAddress = new Uri($"{App.Uri}")
            };

        }

我的请求之一示例：

   public async Task<User> GetProfileSetup()
        {
            try
            {
                if (CrossConnectivity.Current.IsConnected)
                {
                    string token = DependencyService.Get<ISharedFunctions>().GetAccessToken();

                    client.DefaultRequestHeaders.Clear();
                    client.DefaultRequestHeaders.Add("Accept", "application/json");
                    client.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);

                    var response = await client.GetAsync(@"api/User/GetProfilSetup");
                    if (response.IsSuccessStatusCode)
                    {
                        string jsonMessage;
                        using (Stream responseStream = await response.Content.ReadAsStreamAsync())
                        {
                            jsonMessage = new StreamReader(responseStream).ReadToEnd();
                        }
                        User user = JsonConvert.DeserializeObject<User>(jsonMessage);


                        return user;
                    }
                    else
                    {
                        var m = response.Content.ToString();
                        return null;
                    }

                }
                else
                {
                    return null;
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
                string error = ex.Message;
                return null;

            }
        }

我的想法是在一个地方检查每个响应（响应状态代码）。我需要这个来抛出警报错误，刷新令牌等。有没有可能的方法？我想控制每个请求/响应。

Answer 1

如果有人对此有问题，只需要实现自定义处理程序，谁将继承表单 DelegatingHandler。我的代码示例：

  public class StatusCodeHandler : DelegatingHandler
    {
        public StatusCodeHandler(HttpMessageHandler innerHandler) : base(innerHandler) { }
        public GetStatusCode GetStatusCode = new GetStatusCode();
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            HttpResponseMessage response = null;
                response = await base.SendAsync(request, cancellationToken);
                if (response.IsSuccessStatusCode)
                {
                    return response;
                }
            else
            { 
                var status_code = (int)response.StatusCode;
                GetStatusCode.GetResponseCode(status_code);
            }
            return response;
        }

     }

Answer 2

这与 xamarin 无关，它是 OOP 中的抽象问题。您可以并且应该抽象 HttpClient 及其方法以删除所有样板文件。

示例 - GetAsync<T>(url) 将检查连接，表单请求添加必要的标头，等待响应，检查响应状态，读取响应并最终返回反序列化的响应。这样，如果你想添加缓存层就更容易了。基本 OOP。

抽象你的代码：

public async Task<T> GetAsync(string url)
{
    try
    {
        if (!CrossConnectivity.Current.IsConnected)
        {
            // throw custom exception?
            new NoNetworkException();
        }
        var token = DependencyService.Get<ISharedFunctions>().GetAccessToken();
        client.DefaultRequestHeaders.Clear();
        client.DefaultRequestHeaders.Add("Accept", "application/json");
        client.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);
        var response = await client.GetAsync(url);
        if (!response.IsSuccessStatusCode)
        {
            // read response and throw for logging?
            new InvaidResponseException();// custom exceptions makes it easier for catching
        }
        using (Stream responseStream = await response.Content.ReadAsStreamAsync())
        {
            // there should be an async overload to read too
            var jsonMessage = new StreamReader(responseStream).ReadToEnd();
            return JsonConvert.DeserializeObject<T>(jsonMessage);
        }                
    }
    catch(NoNetworkException ex)
    {
        // handle
    }
    catch(InvaidResponseException ex)
    {
        // handle 
    }
}