c# – 如何从方法外部获得异步Web请求的响应？
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我有点困惑.我试图以异步方式发布到我的Web服务,理想情况下我想启动请求,在UI上显示加载微调器,然后当异步请求完成处理响应时,如果有响应则显示错误,或者用结果做另一个操作.
这是我的代码,我在这里调用请求并传递一些数据.
private void SignInExecute()
{
if (Username == null || Password == null)
{
LoginOutput = "Please provide a username or password.";
}
else
{
this.webService.SendLoginRequest("http://localhost:3000/client_sessions", "username=" + Username + "&password=" + Password);
}
}
这是实际的Web请求代码：
public void SendLoginRequest(string url, string postdata)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.Accept = "application/json";
byte[] byteArray = Encoding.UTF8.GetBytes(postdata);
request.CookieContainer = new CookieContainer();
request.ContentLength = byteArray.Length;
Stream dataStream = request.GetRequestStream();
dataStream.Write(byteArray, 0, byteArray.Length);
dataStream.Close();
((HttpWebRequest)request).KeepAlive = false;
request.BeginGetResponse(new AsyncCallback(GetLoginResponseCallback), request);
}
private static void GetLoginResponseCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
// End the operation
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
Stream streamResponse = response.GetResponseStream();
StreamReader streamRead = new StreamReader(streamResponse);
string responseString = streamRead.ReadToEnd();
Console.WriteLine(responseString);
// Close the stream object
streamResponse.Close();
streamRead.Close();
response.Close();
}
所以总结一下.我希望能够将响应返回给最初调用Web请求启动的对象.有帮助吗？
解决方法:
您需要告诉BeginGetResponse返回到通过SynchronizationContext.Current调用它的相同上下文.像这样的东西(代码没有正确的错误检查,所以你应该正确考虑)(另外,Platinum Azure是正确的,你应该使用一个使你的流正常关闭(并保证)：
在您的SendLoginRequest中：
//Box your object state with the current thread context
object[] boxedItems = new []{request, SynchronizationContext.Current};
request.BeginGetResponse(new AsyncCallback(GetLoginResponseCallback),
boxedItems);
getresponse代码：
private static void GetLoginResponseCallback(IAsyncResult asynchronousResult)
{
//MY UPDATE
//Unbox your object state with the current thread context
object[] boxedItems = asynchronousResult.AsyncState as object[];
HttpWebRequest request = boxedItems[0] as HttpWebRequest;
SynchronizationContext context = boxedItems[1] as SynchronizationContext;
// End the operation
using(HttpWebResponse response =
(HttpWebResponse)request.EndGetResponse(asynchronousResult))
{
using(Stream streamResponse = response.GetResponseStream())
{
using(StreamReader streamRead = new StreamReader(streamResponse))
{
string responseString = streamRead.ReadToEnd();
Console.WriteLine(responseString);
//MY UPDATE
//Make an asynchronous call back onto the main UI thread
//(context.Send for a synchronous call)
//Pass responseString as your method parameter
//If you have more than one object, you will have to box again
context.Post(UIMethodToCall, responseString);
}
}
}
}
实现UI处理
public static void UIMethodCall(object ObjectState)
{
String response = ObjectState as String;
label1.Text = String.Format("Output: {0}", response);
//Or whatever you need to do in the UI...
}
现在,我会先测试一下这个.我对Microsoft实现事件驱动异步的理解是,响应是上下文感知的,并且知道返回哪个上下文.因此,在跳到假设您不在同一个上下文之前,通过尝试更新UI来测试它(如果您不在调用(UI)线程上,这将导致线程上下文异常)
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