我有几十个访问api后端的应用程序，但最近我用netstandard 2玩空白xamarin表单，我无法使用hhtpclient访问后端....在两台机器上试过
var uri = "https://myurl";
var handler = new HttpClientHandler
{
Credentials = new NetworkCredential("user", "P@ssw0rd"),
UseDefaultCredentials = false
};
var formContent = new FormUrlEncodedContent(new[]
{
new KeyValuePair<string, string>("MATRICULA", "2147483647")
});
var client = new HttpClient(handler);
var response = await client.PostAsync(uri, formContent);
var text = await response.Content.ReadAsStringAsync();
异常os postasync行
{System.Net.Http.HttpRequestException：发送请求时发生错误---＆gt; System.Net.WebException：获取响应流时出错（ReadDone2）：ReceiveFailure ---＆gt; System.Exception：在System.Net.WebConnection.HandleError（System.Net.WebExceptionStatus st，System.Exception e，System.String where）[0x00031] in：0
在System.Net.WebConnection.ReadDone（System.IAsyncResult result）[0x00056] in：0
在System.Threading.Tasks.TaskToApm +＆lt;＆gt; c__DisplayClass3_0.b__0（）[0x00000] in：0
在System.Threading.Tasks.AwaitTaskContinuation.InvokeAction（System.Object state）[0x00000] in：0
在System.Threading.ExecutionContext.RunInternal（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback callback，System.Object state，System.Boolean preserveSyncCtx）[0x00071] in：0
在System.Threading.ExecutionContext.Run（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback回调，System.Object状态，System.Boolean preserveSyncCtx）[0x00000] in：0
在System.Threading.Tasks.AwaitTaskContinuation.RunCallback（System.Threading.ContextCallback回调，System.Object状态，System.Threading.Tasks.Task＆amp; currentTask）[0x0001a] in：0
在System.Threading.Tasks.AwaitTaskContinuation.Run（System.Threading.Tasks.Task任务，System.Boolean canInlineContinuationTask）[0x0000a] in：0
在System.Threading.Tasks.Task.FinishContinuations（）[0x000b1] in：0
在System.Threading.Tasks.Task.FinishStageThree（）[0x0003c] in：0
在System.Threading.Tasks.Task 1[TResult].TrySetResult (TResult result) [0x0004f] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Runtime.CompilerServices.AsyncTaskMethodBuilder 1 [TResult] .SetResult（TResult result）[0x0003e] in：0
在Mono.Net.Security.MobileAuthenticatedStream + d__58.MoveNext（）[0x001ee] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.InvokeMoveNext（System.Object stateMachine）[0x00000] in：0
在System.Threading.ExecutionContext.RunInternal（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback callback，System.Object state，System.Boolean preserveSyncCtx）[0x00071] in：0
在System.Threading.ExecutionContext.Run（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback回调，System.Object状态，System.Boolean preserveSyncCtx）[0x00000] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.Run（）[0x00024] in：0
在System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction（System.Action action，System.Boolean allowInlining，System.Threading.Tasks.Task＆amp; currentTask）[0x0001c] in：0
在System.Threading.Tasks.Task.FinishContinuations（）[0x00068] in：0
在System.Threading.Tasks.Task.FinishStageThree（）[0x0003c] in：0
在System.Threading.Tasks.Task 1[TResult].TrySetResult (TResult result) [0x00000] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Runtime.CompilerServices.AsyncTaskMethodBuilder 1 [TResult] .SetResult（TResult result）[0x00000] in：0
在Mono.Net.Security.AsyncProtocolRequest + d__23.MoveNext（）[0x000dd] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.InvokeMoveNext（System.Object stateMachine）[0x00000] in：0
在System.Threading.ExecutionContext.RunInternal（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback callback，System.Object state，System.Boolean preserveSyncCtx）[0x00071] in：0
在System.Threading.ExecutionContext.Run（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback回调，System.Object状态，System.Boolean preserveSyncCtx）[0x00000] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.Run（）[0x00024] in：0
在System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction（System.Action action，System.Boolean allowInlining，System.Threading.Tasks.Task＆amp; currentTask）[0x0001c] in：0
在System.Threading.Tasks.Task.FinishContinuations（）[0x00068] in：0
在System.Threading.Tasks.Task.FinishStageThree（）[0x0003c] in：0
在System.Threading.Tasks.Task 1[TResult].TrySetResult (TResult result) [0x0004f] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Runtime.CompilerServices.AsyncTaskMethodBuilder 1 [TResult] .SetResult（TResult result）[0x0003e] in：0
在System.Runtime.CompilerServices.AsyncTaskMethodBuilder 1[TResult].SetResult (System.Threading.Tasks.Task 1 [TResult] completedTask）[0x00010] in：0
在System.Runtime.CompilerServices.AsyncTaskMethodBuilder.SetResult（）[0x00000] in：0
在Mono.Net.Security.AsyncProtocolRequest + d__24.MoveNext（）[0x001d8] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.InvokeMoveNext（System.Object stateMachine）[0x00000] in：0
在System.Threading.ExecutionContext.RunInternal（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback callback，System.Object state，System.Boolean preserveSyncCtx）[0x00071] in：0
在System.Threading.ExecutionContext.Run（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback回调，System.Object状态，System.Boolean preserveSyncCtx）[0x00000] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.Run（）[0x00024] in：0
在System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction（System.Action action，System.Boolean allowInlining，System.Threading.Tasks.Task＆amp; currentTask）[0x0001c] in：0
在System.Threading.Tasks.Task.FinishContinuations（）[0x00068] in：0
在System.Threading.Tasks.Task.FinishStageThree（）[0x0003c] in：0
在System.Threading.Tasks.Task 1[TResult].TrySetResult (TResult result) [0x0004f] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Runtime.CompilerServices.AsyncTaskMethodBuilder 1 [TResult] .SetResult（TResult result）[0x0003e] in：0
在Mono.Net.Security.AsyncProtocolRequest + d__25.MoveNext（）[0x00169] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.InvokeMoveNext（System.Object stateMachine）[0x00000] in：0
在System.Threading.ExecutionContext.RunInternal（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback callback，System.Object state，System.Boolean preserveSyncCtx）[0x00071] in：0
在System.Threading.ExecutionContext.Run（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback回调，System.Object状态，System.Boolean preserveSyncCtx）[0x00000] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.Run（）[0x00024] in：0
在System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction（System.Action action，System.Boolean allowInlining，System.Threading.Tasks.Task＆amp; currentTask）[0x0001c] in：0
在System.Threading.Tasks.Task.FinishContinuations（）[0x00068] in：0
在System.Threading.Tasks.Task.FinishStageThree（）[0x0003c] in：0
在System.Threading.Tasks.Task 1[TResult].TrySetResult (TResult result) [0x0004f] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Runtime.CompilerServices.AsyncTaskMethodBuilder 1 [TResult] .SetResult（TResult result）[0x0003e] in：0
在Mono.Net.Security.MobileAuthenticatedStream + d__66.MoveNext（）[0x0017c] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.InvokeMoveNext（System.Object stateMachine）[0x00000] in：0
在System.Threading.ExecutionContext.RunInternal（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback callback，System.Object state，System.Boolean preserveSyncCtx）[0x00071] in：0
在System.Threading.ExecutionContext.Run（System.Threading.ExecutionContext executionContext，System.Threading.ContextCallback回调，System.Object状态，System.Boolean preserveSyncCtx）[0x00000] in：0
在System.Runtime.CompilerServices.AsyncMethodBuilderCore + MoveNextRunner.Run（）[0x00024] in：0
在System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction（System.Action action，System.Boolean allowInlining，System.Threading.Tasks.Task＆amp; currentTask）[0x0001c] in：0
在System.Threading.Tasks.Task.FinishContinuations（）[0x00068] in：0
在System.Threading.Tasks.Task.FinishStageThree（）[0x0003c] in：0
在System.Threading.Tasks.Task 1[TResult].TrySetResult (TResult result) [0x0004f] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Threading.Tasks.TaskFactory 1 + FromAsyncTrimPromise 1[TResult,TInstance].Complete (TInstance thisRef, System.Func 3 [T1，T2，TResult] endMethod，System.IAsyncResult asyncResult，System.Boolean requiresSynchronization）[0x0000d] in：0
在System.Threading.Tasks.TaskFactory 1+FromAsyncTrimPromise 1 [TResult，TInstance] .CompleteFromAsyncResult（System.IAsyncResult asyncResult）[0x00073] in：0
在System.Net.Sockets.SocketAsyncResult +＆lt;＆gt; c.b__27_0（System.Object state）[0x00000] in：0
在System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem（）[0x00015] in：0
在System.Threading.ThreadPoolWorkQueue.Dispatch（）[0x00074]中：0
at ObjCRuntime.Runtime.ThreadPoolDispatcher（System.Func 1[TResult] callback) [0x00006] in <b7935acd70e343049845d6fd73e5ec44>:0
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback () [0x00009] in <cf9013b38a4e4129bd64785080dd2844>:0
at System.Net.WebConnection.HandleError (System.Net.WebExceptionStatus st, System.Exception e, System.String where) [0x00031] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/System/System.Net/WebConnection.cs:439
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.EndGetResponse (System.IAsyncResult asyncResult) [0x00059] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/System/System.Net/HttpWebRequest.cs:1033
at System.Threading.Tasks.TaskFactory 1 [TResult] .FromAsyncCoreLogic（System.IAsyncResult iar，System.Func 2[T,TResult] endFunction, System.Action 1 [T] endAction，System.Threading.Tasks.Task {{ 1}} 1 + ConfiguredTaskAwaiter [TResult] .GetResult（）[0x00000] in：0
在/Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/System.Net.Http中的System.Net.Http.HttpClientHandler + d__64.MoveNext（）[0x003d3] /System.Net.Http/HttpClientHandler.cs:402
---内部异常堆栈跟踪结束---
在/Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/System.Net.Http中的System.Net.Http.HttpClientHandler + d__64.MoveNext（）[0x0046c] /System.Net.Http/HttpClientHandler.cs:406
---从抛出异常的先前位置开始的堆栈跟踪结束---
在/Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime中的System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw（）[0x0000c]中/exceptionservices/exceptionservicescommon.cs:152
在/Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class中的System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess（System.Threading.Tasks.Task任务）[0x00037] /referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187
在/Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class中的System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（System.Threading.Tasks.Task任务）[0x00028] /referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156
在/Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class中的System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd（System.Threading.Tasks.Task任务）[0x00008] /referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128
在System.Runtime.CompilerServices.ConfiguredTaskAwaitable 1[TResult] promise, System.Boolean requiresSynchronization) [0x0000f] in <cf9013b38a4e4129bd64785080dd2844>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:152
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00037] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable 1 [TResult] .GetResult（）[0x00000] in：0
在App6.MainPage + d__1.MoveNext（）[0x000b0]在C：\ Users \ gilbe \ source \ repos \ App6 \ App6 \ App6 \ MainPage.xaml.cs：38}
答案 0 :(得分：0)
转到Android visual studio项目属性。然后转到Android选项，然后进入高级（在底部），然后执行HttpClient并从列表中选择Android。