C# · 12月 25, 2021

c# – 从任务中的异步HttpWebRequest调用捕获异常

我如何在下面的方法中捕获异常? private static Task<string> MakeAsyncRequest(string url) { if (!url.Contains(“http”)) url = “http://” + url; HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); request.UserAgent = “Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)”; request.Accept = “text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8”; request.Method = “GET”; request.KeepAlive = false; request.ProtocolVersion = HttpVersion.Version10; Task<WebResponse> task = Task.Factory.FromAsync( request.BeginGetResponse,asyncResult => request.EndGetResponse(asyncResult),(object)null); return task.ContinueWith(t => FinishWebRequest(t.Result)); }

我得到404,403等错误的具体地点是:

Task<WebResponse> task = Task.Factory.FromAsync( request.BeginGetResponse,(object)null);

我无法弄清楚如何处理它们

解决方法 您的错误可能发生在您的委托调用request.EndGetResponse(asyncResult)中.

但是您可以使用以下命令创建任务:

Task<WebResponse> task = Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse,request.EndGetResponse,null);

这应该传播任务的任何例外.

您可以在ContinueWith委托中检查错误:

return task.ContinueWith(t =>{ if (t.IsFaulted) { //handle error Exception firstException = t.Exception.InnerExceptions.First(); } else { return FinishWebRequest(t.Result); }});

或者,如果您使用的是C#5,则可以使用async / await创建MakeAsyncRequest.这将为您从AggregateException中解除异常:

private static async Task<string> MakeAsyncRequest(string url){ if (!url.Contains(“http”)) url = “http://” + url; HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); request.UserAgent = “Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)”; request.Accept = “text/html,*/*;q=0.8”; request.Method = “GET”; request.KeepAlive = false; request.ProtocolVersion = HttpVersion.Version10; Task<WebResponse> task = Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse,null); WebResponse response = await task; return FinishWebRequest(response);}