HttpClient PostAsync() 在 Xamarin Forms 应用程序中不起作用

Question

在我的 Xamarin Forms 应用程序中

我正在尝试将 JSON 字符串发布到我的 Web 服务，即 RestFul API 当我使用以下代码时：

public static async Task<bool> SaveRolAsync(Methods Method, Role Rol)
    {
        try
        {
            HttpClient client = new HttpClient();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            var uri = ("http://myservice.com/roles/");
            HttpResponseMessage response = null;

            try
            {
                var jSettings = new JsonSerializerSettings();
                jSettings.NullValueHandling = NullValueHandling.Ignore;
                jSettings.MissingMemberHandling = MissingMemberHandling.Ignore;

                var JsonData = JsonConvert.SerializeObject(Rol);
                var RoleContent = new StringContent(JsonData, Encoding.UTF8, "application/json");

                if (Method == Methods.PUT || Method == Methods.PATCH)
                {
                    response = await client.PutAsync(uri, RoleContent);
                }

                if (Method == Methods.POST)
                {
                    response = await client.PostAsync(uri, RoleContent);
                }

                if (Method == Methods.DELETE)
                {
                    throw new NotImplementedException();
                }

                return response.IsSuccessStatusCode;

            }
            catch (JsonException jse)
            {
                return false;
            }
        }
        catch (Exception ex)
        {
            // Exceptions Throws here
            // @T This line I got The request requires buffering data to succeed
            return false;
        }
    }

抛出异常：

请求需要缓冲数据才能成功

堆栈跟踪：

{System.Net.WebException：该请求需要缓冲数据以 成功。 在 System.Net.HttpWebRequest.EndGetResponse (System.IAsyncResult asyncResult) [0x00064] 中 :0 于 System.Threading.Tasks.TaskFactory

1[TResult].FromAsyncCoreLogic (System.IAsyncResult iar, System.Func

2[T,TResult] endFunction, 系统.Action

1[T] endAction, System.Threading.Tasks.Task

1[TResult] 承诺，System.Boolean 需要同步）[0x00014] 中 :0 --- 从先前抛出异常的位置开始的堆栈跟踪结束 --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] 在 :0 处 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task 任务) [0x0004e] 中 :0 于 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task 任务) [0x0002e] 中 :0 于 System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task 任务) [0x0000b] 中 :0 于 System.Runtime.CompilerServices.ConfiguredTaskAwaitable

1+ConfiguredTaskAwaiter[TResult].GetResult () [0x00000] in <a66f207c1e5949e9a252c01e27bbd34e>:0    at System.Net.Http.HttpClientHandler+<SendAsync>c__async0.MoveNext () [0x0041e] in <566d6cf6576345098cb5e08ad43d5e78>:0  --- End of stack trace from previous location where exception was thrown ---   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <a66f207c1e5949e9a252c01e27bbd34e>:0    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <a66f207c1e5949e9a252c01e27bbd34e>:0    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <a66f207c1e5949e9a252c01e27bbd34e>:0    at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <a66f207c1e5949e9a252c01e27bbd34e>:0    at System.Runtime.CompilerServices.ConfiguredTaskAwaitable

1+ConfiguredTaskAwaiter[TResult].GetResult () [0x00000] 在 :0 处 System.Net.Http.HttpClient+c__async0.MoveNext() [0x000f3] 在 <566d6cf6576345098cb5e08ad43d5e78>:0 --- 从先前抛出异常的位置开始的堆栈跟踪结束 --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] 在 :0 处 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task 任务) [0x0004e] 中 :0 于 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task 任务) [0x0002e] 中 :0 于 System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task 任务) [0x0000b] 中 :0 在 System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] 在 :0 处 MyAPP.Webservice+d__4.MoveNext()[0x000d0]中 C:\MyProject\Classes\Webservice.cs:140 }

**还尝试过：SendAsync() Ty M. Wiśnicki **

public static async Task<bool> SaveRolAsync(MediwareLib.Methods Method, Role Rol)
    {
        try
        {
            HttpClient client = new HttpClient();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            var uri = (BaseRequestUrl + "roles/");
            HttpResponseMessage response = null;
            var request = new HttpRequestMessage();

            try
            {
                var jSettings = new JsonSerializerSettings();
                jSettings.NullValueHandling = NullValueHandling.Ignore;
                jSettings.MissingMemberHandling = MissingMemberHandling.Ignore;

                var JsonData = JsonConvert.SerializeObject(Rol);

                var RoleContent = new StringContent(JsonData, Encoding.UTF8, "application/json");

                if (Method == MediwareLib.Methods.PUT || Method == MediwareLib.Methods.PATCH)
                {
                    request = new HttpRequestMessage(HttpMethod.Put, uri);
                    request.Content = RoleContent;

                    response = await client.SendAsync(request,
                    HttpCompletionOption.ResponseHeadersRead);
                }

                if (Method == MediwareLib.Methods.POST)
                {
                    request = new HttpRequestMessage(HttpMethod.Post, uri);
                    request.Content = RoleContent;

                    response = await client.SendAsync(request,
                    HttpCompletionOption.ResponseHeadersRead);
                }

                if (Method == MediwareLib.Methods.DELETE)
                {
                    throw new NotImplementedException();
                    // response = await client.DeleteAsync(uri + Rol.Id);
                }

                return response.IsSuccessStatusCode;

            }
            catch (JsonException jse)
            {
                Globals.Log("SaveRolAsync: " + jse.ToString());
                return false;
            }
        }
        catch (Exception ex)
        {
            Globals.Log("SaveRolAsync: " + ex.ToString());
            return false;
        }

    }

Answer 1

由于您正在使用

.Result

或

.Wait

或

await

这最终会导致代码中出现 死锁。

您可以在

ConfigureAwait(false)

方法中使用

async

防止死锁

像这样：

response = await client.PostAsync(uri, RoleContent).ConfigureAwait(false);

您可以尽可能使用

ConfigureAwait(false)

来实现“不阻止异步代码”。

Answer 2

您可以使用

SendAsync()

和

HttpCompletionOption.ResponseHeadersRead

来代替

PostAsync()

，问题在于读取响应，它在未准备好时读取。

var request = new HttpMessageRequest(yourUrl);
request.Content = yourContent;
var response = await client.SendAsync(request, 
HttpCompletionOption.ResponseHeadersRead);

使用

HttpCompletionOption.ResponseHeadersRead

响应可用且标头被读取后，操作应立即完成。内容还没读完。

编辑 您可以使用

HttpWebRequest

代替

HttpClient

   public async Task<string> PostTest(object sampleData, string uri)
    {
        var request = (HttpWebRequest) WebRequest.Create(new Uri(uri));
        request.ContentType = "application/json";
        request.Method = "POST";
        request.Timeout = 4000; //ms
        var itemToSend = JsonConvert.SerializeObject(sampleData);
        using (var streamWriter = new StreamWriter(await request.GetRequestStreamAsync()))
        {
            streamWriter.Write(itemToSend);
            streamWriter.Flush();
            streamWriter.Dispose();
        }

        // Send the request to the server and wait for the response:  
        using (var response = await request.GetResponseAsync())
        {
            // Get a stream representation of the HTTP web response:  
            using (var stream = response.GetResponseStream())
            {
                var reader = new StreamReader(stream);
                var message = reader.ReadToEnd();
                return message;
            }
        }
    }