Question

如何使用Async / Await模式转换我的传统HttpWebRequest“POST”调用，这里有我附加我当前的代码，任何人请帮我转换此代码使用Windows Phone 8的Async / Await模式。 / p>

public 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);
    byte[] requestBody = Encoding.UTF8.GetBytes(serializedResult);

    request.BeginGetRequestStream(GetRequestStreamCallback, new object[] { request, requestBody });

}

private void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
    var request = (HttpWebRequest)((object[])asynchronousResult.AsyncState)[0];
    using (var postStream = request.EndGetRequestStream(asynchronousResult))
    {
        var byteArray = (byte[])((object[])asynchronousResult.AsyncState)[1];

        // Write to the request stream.
        postStream.Write(byteArray, 0, byteArray.Length);

    }
    request.BeginGetResponse(GetResponseCallback, request);
}

private void GetResponseCallback(IAsyncResult asynchronousResult)
{
    var request = (HttpWebRequest)asynchronousResult.AsyncState;
    try
    {
        var response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        if (response != null)
        {
            var reader = new StreamReader(response.GetResponseStream());
            string responseString = reader.ReadToEnd();
            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);

    }
}

Answer 1

由于Windows Phone 8似乎不提供您需要的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：

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 - 这是获取await友好包装器的首选方法，该包装器基于基于APM的异步API，例如WebRequest提供的异步API。这比使用其他人建议的Task.Factory.StartNew更有效，因为这会启动一个新线程，而这不需要。

有了这个，您现在可以像在可以使用这些TAP风格的方法的平台上那样编写代码（例如Windows 8商店应用程序，桌面应用程序等）：

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:条评论的四行 - 这些显示了我进行更改的位置。我已经将你的方法折叠为一个，因为这是a）一旦你使用async和await和b）可能比尝试使用状态参数将事物从一个方法传递到下一个方法容易得多

请注意，这些中的第二个和第四个实际上使您以前同步执行的操作异步化：将数据写入请求流，并从响应流中读取数据。对于小请求，这可能无关紧要，但如果正在传输大量数据，则可能会阻止对Write或ReadToEnd的同步调用。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上提供了这些方法，因此无需编写任何扩展方法即可实现。

Answer 2

我是社区的新手，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);
        });
    }
}

Answer 3

这应该做的工作：

    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);
        }
    }

使用Async和Await转换普通的Http Post Web请求

3 个答案: