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));
}
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);
}
