我一直在摸不着头脑。我不知道抛出这个异常的地方。我到底应该抓住这个例外?这是一个System.Net.WebException
。我想我只是没有得到Task和async / await。我知道我正在创建其他线程,这很好,但是我在哪里处理异常?
The remote server returned an error: (403) Forbidden.
以下是代码:
public async void sendRequest(string database, string table, string where, bool isPost, int deviceType)
{
string urlQuery = Constants.URL_QUERY + database + "/" + table + "?" + where;
Debug.WriteLine("URL Query: " + urlQuery);
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(urlQuery);
request.Method = isPost ? "POST" : "GET";
request.ContentType = "application/json";
try
{
Debug.WriteLine("getting response");
WebResponse response = await makeAsyncRequest(request);
Debug.WriteLine("response obtained");
finishRequest(response);
}
catch (WebException e)
{
Debug.WriteLine("WebException caught");
}
}
private async static Task<WebResponse> makeAsyncRequest(HttpWebRequest req)
{
Task<WebResponse> task = Task.Factory.FromAsync<WebResponse>(req.BeginGetResponse, req.EndGetResponse, null);
await task.ContinueWith(t =>
{
if (t.IsFaulted)
{
Debug.WriteLine("It's faulted.");
t.Exception.Handle((x) =>
{
if (x is WebException)
{
Debug.WriteLine("It's a web exception");
return true;
}
Debug.WriteLine("Exception?: " + x);
return false;
});
}
});
Debug.WriteLine("returning task");
return task.Result;
}
private static void finishRequest(WebResponse response)
{
Debug.WriteLine("finishRequest called");
}
以下是我在“输出”窗口中看到的内容:
2014-10-07 14:05:05.104 FormsTemplateiOS[1568:53280] getting response
[0:] getting response
Thread started: #3
Thread started: <Thread Pool> #4
Thread started: <Thread Pool> #5
Thread started: <Thread Pool> #6
Thread started: <Thread Pool> #7
Thread started: #8
[0:]
2014-10-07 14:05:05.681 FormsTemplateiOS[1568:53326] It's faulted.
[0:] It's faulted.
[0:]
2014-10-07 14:05:05.804 FormsTemplateiOS[1568:53326] It's a web exception
[0:] It's a web exception
Unhandled Exception:
System.Net.WebException: The remote server returned an error: (403) Forbidden.
Unhandled Exception:
System.Net.WebException: The remote server returned an error: (403) Forbidden.
at System.Net.HttpWebRequest.CheckFinalStatus (System.Net.WebAsyncResult result) [0x0033b] in ///Library/Frameworks/Xamarin.iOS.framework/Versions/8.0.0.63/src/mono/mcs/class/System/System.Net/HttpWebRequest.cs:1718
at System.Net.HttpWebRequest.SetResponseData (System.Net.WebConnectionData data) [0x00165] in ///Library/Frameworks/Xamarin.iOS.framework/Versions/8.0.0.63/src/mono/mcs/class/System/System.Net/HttpWebRequest.cs:1485
The program 'Mono' has exited with code 0 (0x0).
Debugging session ended.
编辑:
我根据Stephen Cleary的建议更新了makeAsyncRequest(HttpWebRequest)
。我仍然遇到同样的问题。
private async static Task<WebResponse> makeAsyncRequest(HttpWebRequest req)
{
Task<WebResponse> task = Task.Factory.FromAsync<WebResponse>(req.BeginGetResponse, req.EndGetResponse, null);
try
{
return await task;
}
catch (WebException e)
{
Debug.WriteLine("It's a WebException");
}
catch (Exception e)
{
Debug.WriteLine("Other Exception");
}
return null;
}
输出窗口:
2014-10-07 14:32:08.385 FormsTemplateiOS[1588:57008] getting response
[0:] getting response
Thread started: #3
Thread started: <Thread Pool> #4
Thread started: <Thread Pool> #5
Thread started: <Thread Pool> #6
Thread started: <Thread Pool> #7
Thread started: #8
Unhandled Exception:
System.Net.WebException: The remote server returned an error: (403) Forbidden.
Unhandled Exception:
System.Net.WebException: The remote server returned an error: (403) Forbidden.
at System.Net.HttpWebRequest.CheckFinalStatus (System.Net.WebAsyncResult result) [0x0033b] in ///Library/Frameworks/Xamarin.iOS.framework/Versions/8.0.0.63/src/mono/mcs/class/System/System.Net/HttpWebRequest.cs:1718
at System.Net.HttpWebRequest.SetResponseData (System.Net.WebConnectionData data) [0x00165] in ///Library/Frameworks/Xamarin.iOS.framework/Versions/8.0.0.63/src/mono/mcs/class/System/System.Net/HttpWebRequest.cs:1485
The program 'Mono' has exited with code 0 (0x0).
Debugging session ended.
答案 0 :(得分:4)
我知道我正在创建其他线程,这很棒,所有
不,实际上。您可能需要阅读我的async
intro。
此外:
async void
。await
代替ContinueWith
。您还可以找到我的async
best practices文章。
private async static Task<WebResponse> MakeRequestAsync(HttpWebRequest req)
{
Task<WebResponse> task = Task.Factory.FromAsync<WebResponse>(req.BeginGetResponse, req.EndGetResponse, null);
try
{
return await task;
}
catch (WebException ex)
{
Debug.WriteLine("It's a web exception");
}
catch (Exception ex)
{
Debug.WriteLine("It's not a web exception.");
}
}
最后请注意,请考虑使用HttpClient
代替HttpWebRequest
。 HttpClient
专为async
用途而设计。