HttpClient c# - 在 SendASync 取消了一个任务

Question

即使我增加了超时，我也会收到TaskCanceledException。令人惊讶的是它甚至不总是发生，异常只在某个时候发生，我无法找到重现错误的模式。我添加了用于进行网络调用的异常跟踪和代码。

public static void getResponseFromUrlAsync<T>(T payload, string url,
     Action<string> onSuccess, Action<string> onFailure)
{
    string contentType = "application/json";
    httpClient = new HttpClient();
    httpClient.Timeout = TimeSpan.FromMinutes(30);
    HttpRequestMessage requestMsg = new HttpRequestMessage();
    requestMsg.RequestUri = new Uri(NetworkCallUrls.baseUri + url);
    Utils.debugLog("Url", NetworkCallUrls.baseUri + url);

    // try
    //{
    string auth = "Bearer " + Objects.GlobalVars.GetValue<string>("access_token"); // //"x1VwaR1otS66ZCTlgtv3X9aaSNpDOn"; //
    httpClient.DefaultRequestHeaders.Add("Authorization", auth);
    requestMsg.Method = HttpMethod.Post;

    requestMsg.Content = new StringContent(
                   Utils.stringifyData(payload),
                   Encoding.UTF8,
                   contentType);

    httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));//ACCEPT header

    makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction(requestMsg, onSuccess, onFailure, progressBarStatus);
}

internal static void disposeConnection(HttpClient httpClient)
{
    httpClient.Dispose();
    httpClient = null;
}

private static async void makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction(
    HttpRequestMessage requestMsg, Action<string> onSuccess,
    Action<string> onFailure, Action<bool> progressBarStatus)
{
    Utils.debugLog("IN MAKE NETWORK CALL 1");
    HttpResponseMessage response = await httpClient.SendAsync(requestMsg);
    Utils.debugLog("IN MAKE NETWORK CALL 2");
    ResponseStatus responseStatus = checkResponseStatusAndExecuteActionAccordinglyAsync(response);
    Utils.debugLog("IN MAKE NETWORK CALL 3");
    if (responseStatus.isSuccess)
    {
        Utils.debugLog("IN MAKE NETWORK CALL 4");
        string responseString = await response.Content.ReadAsStringAsync();
        Utils.debugLog("IN MAKE NETWORK CALL 5");
        onSuccess(responseString);
        Utils.debugLog("IN MAKE NETWORK CALL 6");
    }
    else
    {
        Utils.debugLog("IN MAKE NETWORK CALL 7");
        onFailure(responseStatus.failureResponse);
        Utils.debugLog("IN MAKE NETWORK CALL 8");
    }
    Utils.debugLog("IN MAKE NETWORK CALL 9");
    disposeConnection(httpClient);
    Utils.debugLog("IN MAKE NETWORK CALL 10");
}

我正在使用上面的代码进行 API 调用，我在 HttpResponseMessage response = await httpClient.SendAsync(requestMsg); 行中收到了 TaskCanceledException。

有人可以帮我解决这个问题吗？我在互联网上搜索并增加了超时时间，但没有用。

Answer 1

我希望能帮助您解决问题的一些 cmets：

1. async 方法应该返回 Task 如果你没有什么要返回，而不是 void。您不必实际返回 Task 对象，编译器会处理它。唯一的例外是 WinForms 和 WebForms 事件处理程序。
2. 您的getResponseFromUrlAsync 方法不是异步的，但它应该是。您应该添加一个async 修饰符，并返回Task。然后，await makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction(...)。这可能是您的问题的根源 - 您在返回之前没有等待异步操作完成。
3. 一般来说，您的httpClient 变量似乎是在某个地方全局定义的。您很容易遇到 NullReferenceException，因为即使不先调用 getResponseFromUrlAsync 也可以调用 makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction，disposeConnection 也可以。如果您的类始终使用httpClient，请在构造函数或声明中对其进行初始化。如果不是，请在方法开始时检查它是否为 null。

Answer 2

您应该等待makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction 方法和getResponseFromUrlAsync 方法。这意味着您需要将返回类型从void 更改为Task：

public static async Task getResponseFromUrlAsync<T>(T payload, string url, Action<string> onSuccess, Action<string> onFailure)
{
    string contentType = "application/json";
    httpClient = new HttpClient();
    httpClient.Timeout = TimeSpan.FromMinutes(30);
    HttpRequestMessage requestMsg = new HttpRequestMessage();
    requestMsg.RequestUri = new Uri(NetworkCallUrls.baseUri + url);
    Utils.debugLog("Url", NetworkCallUrls.baseUri + url);


    string auth = "Bearer " + Objects.GlobalVars.GetValue<string>("access_token"); // //"x1VwaR1otS66ZCTlgtv3X9aaSNpDOn"; //
    httpClient.DefaultRequestHeaders.Add("Authorization", auth);
    requestMsg.Method = HttpMethod.Post;

    requestMsg.Content = new StringContent(
                   Utils.stringifyData(payload),
                   Encoding.UTF8,
                   contentType);

    httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));//ACCEPT header

    await makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction(requestMsg, onSuccess, onFailure, progressBarStatus)
        .ConfigureAwait(false);
}

internal static void disposeConnection(HttpClient httpClient)
{
    httpClient.Dispose();
    httpClient = null;
}

private static async Task makeNetworkCallCheckResponseStatusAndExecuteCorrospondingAction(
    HttpRequestMessage requestMsg, Action<string> onSuccess,
    Action<string> onFailure, Action<bool> progressBarStatus)
{
    Utils.debugLog("IN MAKE NETWORK CALL 1");
    HttpResponseMessage response = await httpClient.SendAsync(requestMsg).ConfigureAwait(false);
    Utils.debugLog("IN MAKE NETWORK CALL 2");
    ResponseStatus responseStatus = checkResponseStatusAndExecuteActionAccordinglyAsync(response);
    Utils.debugLog("IN MAKE NETWORK CALL 3");
    if (responseStatus.isSuccess)
    {
        Utils.debugLog("IN MAKE NETWORK CALL 4");
        string responseString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
        Utils.debugLog("IN MAKE NETWORK CALL 5");
        onSuccess(responseString);
        Utils.debugLog("IN MAKE NETWORK CALL 6");
    }
    else
    {
        Utils.debugLog("IN MAKE NETWORK CALL 7");
        onFailure(responseStatus.failureResponse);
        Utils.debugLog("IN MAKE NETWORK CALL 8");
    }
    Utils.debugLog("IN MAKE NETWORK CALL 9");
    disposeConnection(httpClient);
    Utils.debugLog("IN MAKE NETWORK CALL 10");
}

...和await 调用它时的方法：

await getResponseFromUrlAsync<..>(...);