xamarin 上的 HttpClient PostAsync 什么都不做

Question

我有一段代码

var formContent =
    new FormUrlEncodedContent(new[]
    {
        new KeyValuePair<string, string>("grant_type", "password"),
        new KeyValuePair<string, string>("username", _userName),
        new KeyValuePair<string, string>("password", _password)
    });

var response = await InternalClient.PostAsync("/Token", formContent).ConfigureAwait(false);

当我在我的桌面应用程序中使用它时，它工作正常，但同样的部分在 Xamarin.Android 上失败了。我可以从模拟器浏览器访问我的网站，所以这不是没有这两者之间的连接的情况。更有趣的部分 - GetAsync 工作得非常好。由于超时，PostAsync 总是失败并出现 TaskCancelledException。所有 PostAsync 调用根本不会访问服务器。
我执行此操作的活动：

var isAuthSuccess = _mainClient.Authenticate();

isAuthSuccess.ContinueWith(task =>
{
    RunOnUiThread(() =>
    {
        if (isAuthSuccess.Result)
        {
            ReleaseEventHandlers();

            var nav = ServiceLocator.Current.GetInstance<INavigationService>();
            nav.NavigateTo("MainChatWindow", _mainClient);
        }

        button.Enabled = true;
    });
});

还有 Authenticate 方法：

public async Task<bool> Authenticate()
{
    var getTokenOperation = new AsyncNetworkOperation<string>(GetTokenOperation);
    var token = await getTokenOperation.Execute().ConfigureAwait(false);

    if (getTokenOperation.IsCriticalFailure)
    {
        SetCriticalFailure(getTokenOperation.FailureReason);
    }

    if (getTokenOperation.IsFailure == false)
    {
        InternalClient.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);
        return true;
    }

    else
    {
        AuthenticationFailEncounteredEvent("Authentication fail encountered: " + getTokenOperation.FailureReason);
        return false;
    }
}

获取令牌操作：

private async Task<string> GetTokenOperation()
{
    var formContent =
            new FormUrlEncodedContent(new[]
            {
                new KeyValuePair<string, string>("grant_type", "password"),
                new KeyValuePair<string, string>("username", _userName),
                new KeyValuePair<string, string>("password", _password)
            });

    var response = await InternalClient.PostAsync("/Token", formContent).ConfigureAwait(false);
    response.EnsureSuccessStatusCodeVerbose();

    var responseJson = await response.Content.ReadAsStringAsync();

    var jObject = JObject.Parse(responseJson);
    var token = jObject.GetValue("access_token").ToString();

    return token;
}

还有包装器 - AsyncNetworkOperation

public class AsyncNetworkOperation<T>
{
    public bool IsFailure { get; set; }

    public bool IsCriticalFailure { get; set; }

    public string FailureReason { get; set; }

    public bool IsRepeatable { get; set; }

    public int RepeatsCount { get; set; }

    public Func<Task<T>> Method { get; set; }

    public AsyncNetworkOperation(Func<Task<T>> method, int repeatsCount)
    {
        Method = method;
        IsRepeatable = true;
        RepeatsCount = repeatsCount;
    }

    public AsyncNetworkOperation(Func<Task<T>> method)
    {
        Method = method;
    }

    public async Task<T> Execute()
    {
        try
        {
            return await Method().ConfigureAwait(false);
        }

        ...exception handling logics
    }
}

在活动中直接调用 PostAsync 的行为相同 - 等待很长时间，然后由于超时而失败并出现 TaskCancelledException。

Answer 1

对于所有在同一个问题上苦苦挣扎的人 - 这与 SSL（在我的例子中是自签名证书）有关。如果您尝试通过 HTTPS 连接到您的服务器 - 请先尝试使用纯 HTTP，我的应用程序可以正常使用 HTTP，而 HTTPS 挂死。

Answer 2

PostAsync() 也有其他问题，在编辑标题和类似内容方面，它也不像SendAsync() 那样可定制。我会推荐SendAsync()：

HttpRequestMessage  request = new HttpRequestMessage(HttpMethod.Post, "/Token") { Content = formContent };
HttpResponseMessage message = await InternalClient.SendAsync(request, HttpCompletionOption.ResponseContentRead).ConfigureAwait(false);