Question

我有一个方法

 private string MakeRequest

之前已经返回了一个字符串，但现在我在这个方法中有一个异步操作。

request.BeginGetRequestStream(GetRequestStreamCallback, request);

 private void GetRequestStreamCallback(IAsyncResult asynchronousResult)
    {
        var request = (HttpWebRequest)asynchronousResult.AsyncState;

        // End the operation
        var postStream = request.EndGetRequestStream(asynchronousResult);

        // Convert the string into a byte array.
        byte[] byteArray = Encoding.UTF8.GetBytes(request.Connection);

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

        // Start the asynchronous operation to get the response
        request.BeginGetResponse(GetResponseCallback, request);
    }

    private static void GetResponseCallback(IAsyncResult asynchronousResult)
    {
        var request = (HttpWebRequest)asynchronousResult.AsyncState;

        // End the operation
        var response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        var streamResponse = response.GetResponseStream();
        using (var streamRead = new StreamReader(streamResponse))
        {
            var responseString = streamRead.ReadToEnd();
            var trimResponseString = responseString.Trim(); // I need this string to return from MakeRequest
            // Close the stream object
            streamResponse.Close();
            streamRead.Close();

            // Release the HttpWebResponse
            response.Close();
            allDone.Set();
        }
    }

如何将字符串从上次回调返回到MakeRequest？

Answer 1

如果您使用的是.NET 4.5，则可以利用Task中基于WebRequest的方法：

public async Task<string> MakeRequest()
{
    var request = WebRequest.Create(url);

    var postStream = await request.GetRequestStreamAsync();

    // Convert the string into a byte array.
    byte[] byteArray = Encoding.UTF8.GetBytes(request.Connection);

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

    var response = (HttpWebResponse)(await request.GetResponseAsync());
    var streamResponse = response.GetResponseStream();

    using (var streamRead = new StreamReader(streamResponse))
    {
        var responseString = streamRead.ReadToEnd();
        var trimResponseString = responseString.Trim(); // I need this string to return from MakeRequest
        // Close the stream object
        streamResponse.Close();
        streamRead.Close();

        // Release the HttpWebResponse
        response.Close();
        allDone.Set();

        return trimResponseString;
    }
}

如果你从一个非本身异步的上下文中调用它，你可以调用这个方法，然后同步等待结果：

string result = MakeRequest().GetAwaiter().GetResult();

如何从回调中返回一个字符串？

1 个答案: