使用异步和等待转换普通的 Http Post Web 请求

由于Windows Phone 8似乎没有提供您需要的TAP方法，例如GetRequestStreamAsync首先要做的是编写一个小包装器来为自己提供它们：

public static class WebRequestAsyncExtensions
{
    public static Task<Stream> GetRequestStreamAsync(this WebRequest request)
    {
        return Task.Factory.FromAsync<Stream>(
            request.BeginGetRequestStream, request.EndGetRequestStream, null);
    }
    public static Task<WebResponse> GetResponseAsync(this WebRequest request)
    {
        return Task.Factory.FromAsync<WebResponse>(
            request.BeginGetResponse, request.EndGetResponse, null);
    }
}

请注意 Task.Factory.FromAsync 的使用 - 这是在基于 APM 的异步 API 周围获取await友好包装器的首选方法，例如 WebRequest 提供的包装器。这比使用其他人建议的Task.Factory.StartNew要有效得多，因为这会启动一个新线程，而这不需要。

完成此操作后，您现在可以像在提供这些 TAP 样式方法的平台（例如 Windows 8 应用商店应用程序、桌面应用程序等）上一样编写代码：

public async Task GetEnvironmentVariablesAsync(Action<Credentials> getResultCallback, Action<Exception> getErrorCallback)
{
    CredentialsCallback = getResultCallback;
    ErrorCallback = getErrorCallback;
    var uri = new Uri(BaseUri);
    var request = (HttpWebRequest) WebRequest.Create(uri);
    request.Method = "POST";
    request.ContentType = "application/json";
    var jsonObject = new JObject
    {
        new JProperty("apiKey",_api),
        new JProperty("affiliateId",_affid),
    };
    var serializedResult = JsonConvert.SerializeObject(jsonObject);
    byte[] requestBody = Encoding.UTF8.GetBytes(serializedResult);
    // ASYNC: using awaitable wrapper to get request stream
    using (var postStream = await request.GetRequestStreamAsync())
    {
        // Write to the request stream.
        // ASYNC: writing to the POST stream can be slow
        await postStream.WriteAsync(requestBody, 0, requestBody.Length);
    }
    try
    {
        // ASYNC: using awaitable wrapper to get response
        var response = (HttpWebResponse) await request.GetResponseAsync();
        if (response != null)
        {
            var reader = new StreamReader(response.GetResponseStream());
            // ASYNC: using StreamReader's async method to read to end, in case
            // the stream i slarge.
            string responseString = await reader.ReadToEndAsync();
            Credentails = JsonConvert.DeserializeObject<Credentials>(responseString);
            if (Credentails != null && string.IsNullOrEmpty(Credentails.Err))
                CredentialsCallback(Credentails);
            else
            {
                if (Credentails != null)
                    ErrorCallback(new Exception(string.Format("Error Code : {0}", StorageCredentails.Err)));
            }
        }
    }
    catch (WebException we)
    {
        var reader = new StreamReader(we.Response.GetResponseStream());
        string responseString = reader.ReadToEnd();
        Debug.WriteLine(responseString);
        ErrorCallback(we);
    }
}

请注意带有// ASYNC:注释的四行 - 这些行显示了我进行了更改的位置。我已经将您的方法折叠为一个，因为 a） 一旦您使用 async 和 await，这是可能的，并且 b） 比尝试使用状态参数将内容从一个方法传递到下一个方法要容易得多。

请注意，其中的第二个和第四个实际上使以前同步执行的一些操作异步：将数据写入请求流，以及从响应流中读取数据。对于小型请求，这可能无关紧要，但如果正在传输大量数据，则对Write或ReadToEnd的同步调用可能会阻塞。幸运的是，尽管Windows Phone 8似乎缺少WebRequest上的TAP方法，但它确实在Stream和StreamReader上提供了它们，因此无需编写任何扩展方法即可工作。

社区的新手，所以这是我的第一篇文章。 在这种情况下，您可以使用通用任务返回任何类型。 这在过去对我来说效果很好。

服务器端

public class MyController : ApiController
{
    public Task<string> PostAsync()
    {
        return Task.Factory.StartNew(() =>
        {
            return "populate me with any type and data, but change the type in the response signature.";
        });
    }
}

客户端

public class HomeController : Controller
{
    public Task<ViewResult> Index()
    {
        return Task.Factory.StartNew(() =>
        {
            var model = "use a provider, get some data, or something";
            return View(model);
        });
    }
}

这应该可以完成这项工作：

    public async void GetEnvironmentVariables(Action<Credentials> getResultCallback, Action<Exception> getErrorCallback) {
        CredentialsCallback = getResultCallback;
        ErrorCallback = getErrorCallback;
        var uri = new Uri(BaseUri);
        var request = (HttpWebRequest)WebRequest.Create(uri);
        request.Method = "POST";
        request.ContentType = "application/json";
        var jsonObject = new JObject {
            new JProperty("apiKey", _api),
            new JProperty("affiliateId", _affid),
        };
        var serializedResult = JsonConvert.SerializeObject(jsonObject);
        var requestBody = Encoding.UTF8.GetBytes(serializedResult);
        var requestStream = request.GetRequestStream();
        requestStream.Write(requestBody, 0, requestBody.Length);
        await GetResponse(request);
    }
    private async Task GetResponse(WebRequest request) {
        Stream resStream = null;
        try {
            var response = await request.GetResponseAsync();
            if (response == null) {
                return;
            }
            resStream = response.GetResponseStream();
            if (resStream == null) {
                return;
            }
            var reader = new StreamReader(resStream);
            var responseString = await reader.ReadToEndAsync();
            Credentails = JsonConvert.DeserializeObject<Credentials>(responseString);
            if (Credentails != null && string.IsNullOrEmpty(Credentails.Err)) {
                CredentialsCallback(Credentails);
            }
            else {
                if (Credentails != null) {
                    ErrorCallback(new Exception(string.Format("Error Code : {0}", StorageCredentails.Err)));
                }
            }
        }
        catch (WebException we) {
            if (resStream != null) {
                var reader = new StreamReader(resStream);
                var responseString = reader.ReadToEnd();
                Debug.WriteLine(responseString);
            }
            ErrorCallback(we);
        }
    }