我正在创建一个简单的应用程序来连接到Web服务，我在管理异步请求时遇到了问题。
问题在于ProcessRequest函数，它基本上生成异步HttpWebRequest，并返回HttpWebResponse。由于请求是异步的，我遇到了返回值的问题，并且函数调用了ProcessRequest方法并等待了HttpWebResponse对象。
顺便说一下，请求本身运行完美，已经在函数内部进行了测试，所以我不需要返回一个HttpWebResponse。
我希望我能说清楚，正如我所说，这是我第一次接触c＃,. NET和Windows Phone开发。 （还有WebRequests）
Visual Studio抛出的错误是：
1: Since 'System.AsyncCallback' returns void, a return keyword must not be followed by an object expression
2: Cannot convert lambda expression to delegate type 'System.AsyncCallback' because some of the return types in the block are not implicitly convertible to the delegate return type
这是代码：
namespace SimpleNoteConcept
{
public sealed class SimpleNote
{
private static readonly SimpleNote _instance = new SimpleNote();
private static string _authToken = string.Empty;
private static string _email = string.Empty;
private static string _authQsParams
{
get
{
if (string.IsNullOrEmpty(_authToken)) throw new SimpleNoteConceptAuthorisationException();
return string.Format("auth={0}&email={1}", _authToken, _email);
}
}
private SimpleNote() { }
public static SimpleNote Instance
{
get { return _instance; }
}
public bool Connect(string email, string password)
{
try
{
StringParamCheck("email", email);
StringParamCheck("password", password);
var data = string.Format("email={0}&password={1}", email, password);
var bytes = Encoding.GetEncoding("utf-8").GetBytes(data);
data = Convert.ToBase64String(bytes);
using (var resp = ProcessRequest( loginPath, "POST", content: data))
{
if (resp != null)
{
_authToken = resp.Cookies["auth"].Value;
_email = email;
System.Diagnostics.Debug.WriteLine("Connection established! -> " + _authToken);
return true;
}
return false;
}
}
catch (Exception)
{
throw;
}
}
public void GetIndex(int length = 100, string mark = null, DateTimeOffset? since = null)
{
try
{
string sinceString = null;
if (since.HasValue)
sinceString = Json.DateTimeEpochConverter.DateToSeconds(since.Value);
var queryParams = string.Format("{0}&length={1}&mark={2}&since={3}", _authQsParams, length, mark, sinceString);
using (var resp = ProcessRequest( indexPath, "GET", queryParams))
{
var respContent = ReadResponseContent(resp);
System.Diagnostics.Debug.WriteLine("GetIndex: " + respContent.ToString());
//var notes = JsonConvert.DeserializeObject<Objects.NoteEnumerable<T>>(respContent);
//return notes;
}
}
catch (WebException ex)
{
var resp = (HttpWebResponse)ex.Response;
switch (resp.StatusCode)
{
//401
case HttpStatusCode.Unauthorized:
throw new SimpleNoteConceptAuthorisationException(ex);
default:
throw;
}
}
catch (Exception) { throw; }
}
/// <summary>
/// Generic method to process a request to Simplenote.
/// All publicly expose methods which interact with the store are processed though this.
/// </summary>
/// <param name="requestPath">The path to the request to be processed</param>
/// <param name="method">The HTTP method for the request</param>
/// <param name="content">The content to send in the request</param>
/// <param name="queryParams">Queryparameters for the request</param>
/// <returns>An HttpWebResponse continaing details returned from Simplenote</returns>
private static HttpWebResponse ProcessRequest(string requestPath, string method,
string queryParams = null, string content = null)
{
try
{
var url = string.Format("{0}{1}{2}", "https://", domainPath, requestPath);
if (!string.IsNullOrEmpty(queryParams)) url += "?" + queryParams;
var request = WebRequest.Create(url) as HttpWebRequest;
request.CookieContainer = new CookieContainer();
request.Method = method;
request.BeginGetRequestStream((e) =>
{
using (Stream stream = request.EndGetRequestStream(e))
{
// Write data to the request stream
var bytesBody = Encoding.GetEncoding("utf-8").GetBytes(content);
stream.Write(bytesBody, 0, bytesBody.Length);
stream.Close();
stream.Dispose();
}
request.BeginGetResponse((callback) =>
{
try
{
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(callback);
return response;
}
catch (WebException ex)
{
using (WebResponse Exresponse = ex.Response)
{
HttpWebResponse httpResponse = (HttpWebResponse)Exresponse;
System.Diagnostics.Debug.WriteLine("Error code: {0}", httpResponse.StatusCode);
using (Stream str = Exresponse.GetResponseStream())
{
string text = new StreamReader(str).ReadToEnd();
System.Diagnostics.Debug.WriteLine(text);
}
}
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine("Message: " + ex.Message);
}
}, request);
}, request);
}
catch (Exception)
{
throw;
}
}
/// <summary>
/// Reads the content from the response object
/// </summary>
/// <param name="resp">The response to be processed</param>
/// <returns>A string of the response content</returns>
private static string ReadResponseContent(HttpWebResponse resp)
{
if (resp == null) throw new ArgumentNullException("resp");
using (var sr = new StreamReader(resp.GetResponseStream()))
{
return sr.ReadToEnd();
}
}
/// <summary>
/// String parameter helper method.
/// Checks for null or empty, throws ArgumentNullException if true
/// </summary>
/// <param name="paramName">The name of the paramter being checked</param>
/// <param name="value">The value to check</param>
private void StringParamCheck(string paramName, string value)
{
if (string.IsNullOrEmpty(value)) throw new ArgumentNullException(paramName, "Value must not be null or string.Empty");
}
} // Class End
} // Namespace End
提前致谢！
答案 0 :(得分：1)
您无法像平常一样进行异步编程。这里.Net在不同的线程中运行异步部分，它们如何通信？所以你可以做的是用你的ProcessRequest方法传递一个委托。这将采用HttpWebResponse的参数。
像这样调用你的方法：
Action<HttpWebResponse> actionDelegate = DoAfterGettingResponse;
ProcessRequest(indexPath, "GET", actionDelegate, queryParams);
处理响应的函数
public static void DoAfterGettingResponse(HttpWebResponse resp)
{
if (resp != null)
{
_authToken = resp.Cookies["auth"].Value;
_email = email;
System.Diagnostics.Debug.WriteLine("Connection established! -> " + _authToken);
}
//Do anything else with the response
}
ProcessRequest将拥有新签名。
private static HttpWebResponse ProcessRequest(
string requestPath, string method, Action<HttpWebResponse> reponseDelegate,
string queryParams = null, string content = null)
{
//Do what you are already doing
}
你回复的地方，只是做
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(callback);
responseDelegate(response);
您可以这样做或使用事件，触发传递HttpWebResponse作为参数的事件，并在侦听器中处理响应。