在await客户端上引发了xa marin Form-TaskCanceledException。PostAsync()

Question

非常奇怪的问题（所有代码都在PCL中）。

当我打电话给等待客户端时。PostAsync（） 针对 Web 服务 （API's），我得到了 TaskCanceledException。

需要注意的几点：

这在Android设备上运行良好。只有当我在iOS上运行应用程序时才会发生这种情况，但。。。

…更奇怪的是，我可以让它在iOS上运行，如果我使用不同的（物理）服务器来托管我用等待客户端查询的API。PostAsync（）。

所以，

• https://somedomainname.com - 工作正常
• https://someotherserver.com - 不起作用

更奇怪的是，两台服务器运行完全相同的网络服务，只有0个区别，唯一的区别是服务器位于不同的站点，客户端不同。所以故障不在于被查询的网络服务抛出超时或取消请求。

两台服务器都有有效的（可信的）SSL证书，因此这不是SSL相关的问题。

我卡住了。我已经尝试了< code>ModernHttpClient和增加< code >客户端。TimeSpan。

我还检查了＜code＞ex.CancellationToken。IsCancellationRequested＜/code＞，这是错误的，所以可以很安全地假设这是一段“超时”时间。然而，当我针对该API手动运行PostMan发出的Post请求时，很明显Web服务工作正常（没有超时）。

public class TokenService
{
    private HttpClient client;
    private App app;

    public TokenService()
    {
        //client = new HttpClient();

        client = new HttpClient(new NativeMessageHandler());
        client.Timeout = TimeSpan.FromMinutes(30);

        client.MaxResponseContentBufferSize = 256000;
        app = (App)Application.Current;
    }

    public class TokenResponse
    {
        public String access_token;
        public Int32 expires_in;
    }

    public async Task<String> GetNewToken()
    {
        // check if valid token already stored and within expiry DateTime

        if(Token.BearerToken != null)
        {
            if (Token.expiry > DateTime.Now)
                return Token.BearerToken;
        }

        var tokenUlr = app.WebServicesHostName + "/token";

        var tokenResponse = new TokenResponse();

        try
        {
            var content = new FormUrlEncodedContent(new[]
            {
                // this needs to be stored somewhere safe:
                new KeyValuePair<string, string>("username", "validusernamehere"),
                new KeyValuePair<string, string>("password", "validpasshere")
            });

            var response = await client.PostAsync(tokenUlr, content); // <<***EXCEPTION HERE

            if (response.StatusCode == HttpStatusCode.OK)
            {
                var token = await response.Content.ReadAsStringAsync();

                tokenResponse = JsonConvert.DeserializeObject<TokenResponse>(token);

                Token.BearerToken = tokenResponse.access_token;
                Token.expiry = DateTime.Now.AddSeconds(tokenResponse.expires_in - 30);

                return tokenResponse.access_token;
            }
            else
            {
                return null;

            }
        }
        catch(TaskCanceledException ex)
        {
            String message = ex.Message;
            String source = ex.Source;
            CancellationToken token = ex.CancellationToken;



            return null;
        }
        catch(Exception ex)
        {
            String test = ex.Message;
            return null;
        }
    }
}

例外详情：

{系统。threading . tasks . taskcanceledexception:任务被取消。< br >在系统中。runtime . compiler services . taska waiter . throwfornonsuccess(System。threading . tasks . task task)[0x 0002d]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:179 at System。runtime . compiler services . taskawaiter . handlenonsuccessanddebuggernotification(System。threading . tasks . task task)[0x 0002 e]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:156 at System。runtime . compiler services . taska waiter . validate end(System。threading . tasks . task task)[0x 0000 b]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:128 at System。runtime . compiler services . taska waiter ` 1[t result]。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:357 at System。http . httpclienthandler c _ _ async 0。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/System中的MoveNext () [0x004c1]。Net.Http/System.Net.Http/HttpClientHandler.cs:391

-从引发异常的前一个位置开始的堆栈跟踪结束-在系统中。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/exception services/exceptionservicescommon . cs:143 at System .runtime . compiler services . taska waiter . throwfornonsuccess(System。threading . tasks . task task)[0x 00027]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:176 at System。runtime . compiler services . taskawaiter . handlenonsuccessanddebuggernotification(System。threading . tasks . task task)[0x 0002 e]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:156 at System。runtime . compiler services . taska waiter . validate end(System。threading . tasks . task task)[0x 0000 b]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:128 at System。runtime . compiler services . configuredtaskawaitable ` 1 ConfiguredTaskAwaiter[t result]。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:535 at System。HttpClient c__async0。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/System中的MoveNext () [0x000a9]。Net.Http/System.Net.Http/HttpClient.cs:276

-从引发异常的前一个位置开始的堆栈跟踪结束-在系统中。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/exception services/exceptionservicescommon . cs:143 at System .runtime . compiler services . taska waiter . throwfornonsuccess(System。threading . tasks . task task)[0x 00027]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:176 at System。runtime . compiler services . taskawaiter . handlenonsuccessanddebuggernotification(System。threading . tasks . task task)[0x 0002 e]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:156 at System。runtime . compiler services . taska waiter . validate end(System。threading . tasks . task task)[0x 0000 b]在/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/System/runtime/compiler services/taskawaiter . cs:128 at System。runtime . compiler services . taska waiter ` 1[t result]。/Library/Frameworks/xa marin . IOs . framework/Versions/10 . 4 . 0 . 128/src/mono/MCS/class/reference source/mscorlib/system/runtime/compiler services/taskawaiter . cs:357 at XamarinMO。令牌服务d__4。C:\ Users \ Johns \ one drive \ Sources \ WinMan API和Xamain App \ XamarinMO \ XamarinMO \ XamarinMO \ Services \ token service . cs:67 }中的MoveNext () [0x000e3]

Answer 1

经过许多个小时，我找到了解决方案：

可以通过将项目属性下的 TLS 设置更改为 Mono 而不是 Apple 来修复此问题。这是由于iOS上SSL / TLS的新Apple TLS默认设置中的错误。