WebClient webClient = new WebClient();
webClient.Encoding = Encoding.UTF8;
webClient.DownloadFile(downloadUrl, downloadFile);
有没有办法在该对象上设置无限超时时间？如果没有，是否有人能帮我提供一个替代方法的示例？
在浏览器中URL正常工作，只是需要大约3分钟才会显示出来。
private class MyWebClient : WebClient
{
protected override WebRequest GetWebRequest(Uri uri)
{
WebRequest w = base.GetWebRequest(uri);
w.Timeout = 20 * 60 * 1000;
return w;
}
}
.TotalMilliseconds而不是.Milliseconds！ - Alexander Galkin第一个解决方案对我不起作用，但这里有一些代码确实对我有效。
private class WebClient : System.Net.WebClient
{
public int Timeout { get; set; }
protected override WebRequest GetWebRequest(Uri uri)
{
WebRequest lWebRequest = base.GetWebRequest(uri);
lWebRequest.Timeout = Timeout;
((HttpWebRequest)lWebRequest).ReadWriteTimeout = Timeout;
return lWebRequest;
}
}
private string GetRequest(string aURL)
{
using (var lWebClient = new WebClient())
{
lWebClient.Timeout = 600 * 60 * 1000;
return lWebClient.DownloadString(aURL);
}
}
您需要使用HttpWebRequest而不是WebClient，因为您无法在不扩展WebClient的情况下设置超时（尽管它使用HttpWebRequest）。改用HttpWebRequest将允许您设置超时时间。
HttpWebRequest的Timeout属性完全没有问题。它以毫秒为单位。 - Marcel对于任何需要具有超时功能的WebClient异步/任务方法，建议的解决方案都不可行。以下是有效的解决方案：
public class WebClientWithTimeout : WebClient
{
//10 secs default
public int Timeout { get; set; } = 10000;
//for sync requests
protected override WebRequest GetWebRequest(Uri uri)
{
var w = base.GetWebRequest(uri);
w.Timeout = Timeout; //10 seconds timeout
return w;
}
//the above will not work for async requests :(
//let's create a workaround by hiding the method
//and creating our own version of DownloadStringTaskAsync
public new async Task<string> DownloadStringTaskAsync(Uri address)
{
var t = base.DownloadStringTaskAsync(address);
if(await Task.WhenAny(t, Task.Delay(Timeout)) != t) //time out!
{
CancelAsync();
}
return await t;
}
}
我在这里写了关于完整解决方案的博客（链接）
在拔掉网络电缆时，我无法让 w.Timeout 代码正常工作，它根本不会超时，现在改用 HttpWebRequest 就可以了。
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(downloadUrl);
request.Timeout = 10000;
request.ReadWriteTimeout = 10000;
var wresp = (HttpWebResponse)request.GetResponse();
using (Stream file = File.OpenWrite(downloadFile))
{
wresp.GetResponseStream().CopyTo(file);
}
var wresp = await request.GetResponseAsync();而不是var wresp = (HttpWebResponse)request.GetResponse();，你将再次获得巨大的超时。 - Andrew Boyd为了完整起见，这里是将kisp的解决方案移植到VB的代码（无法在评论中添加代码）。
Namespace Utils
''' <summary>
''' Subclass of WebClient to provide access to the timeout property
''' </summary>
Public Class WebClient
Inherits System.Net.WebClient
Private _TimeoutMS As Integer = 0
Public Sub New()
MyBase.New()
End Sub
Public Sub New(ByVal TimeoutMS As Integer)
MyBase.New()
_TimeoutMS = TimeoutMS
End Sub
''' <summary>
''' Set the web call timeout in Milliseconds
''' </summary>
''' <value></value>
Public WriteOnly Property setTimeout() As Integer
Set(ByVal value As Integer)
_TimeoutMS = value
End Set
End Property
Protected Overrides Function GetWebRequest(ByVal address As System.Uri) As System.Net.WebRequest
Dim w As System.Net.WebRequest = MyBase.GetWebRequest(address)
If _TimeoutMS <> 0 Then
w.Timeout = _TimeoutMS
End If
Return w
End Function
End Class
End Namespace
System.Net.HttpWebRequest并设置Timeout属性，而不是使用System.Net.WebClient。ArgumentOutOfRangeException异常）。Content-Length头部值以确定要下载的文件中的字节数，然后相应地设置后续的GET请求的超时值，或者仅指定一个非常长的超时值，您永远不希望超过该值。使用方法：
using (var client = new TimeoutWebClient(TimeSpan.FromSeconds(10)))
{
return await client.DownloadStringTaskAsync(url).ConfigureAwait(false);
}
类：
using System;
using System.Net;
namespace Utilities
{
public class TimeoutWebClient : WebClient
{
public TimeSpan Timeout { get; set; }
public TimeoutWebClient(TimeSpan timeout)
{
Timeout = timeout;
}
protected override WebRequest GetWebRequest(Uri uri)
{
var request = base.GetWebRequest(uri);
if (request == null)
{
return null;
}
var timeoutInMilliseconds = (int) Timeout.TotalMilliseconds;
request.Timeout = timeoutInMilliseconds;
if (request is HttpWebRequest httpWebRequest)
{
httpWebRequest.ReadWriteTimeout = timeoutInMilliseconds;
}
return request;
}
}
}
但我建议采用更现代的解决方案：
using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
public static async Task<string> ReadGetRequestDataAsync(Uri uri, TimeSpan? timeout = null, CancellationToken cancellationToken = default)
{
using var source = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
if (timeout != null)
{
source.CancelAfter(timeout.Value);
}
using var client = new HttpClient();
using var response = await client.GetAsync(uri, source.Token).ConfigureAwait(false);
return await response.Content.ReadAsStringAsync().ConfigureAwait(false);
}
在超时后，它会抛出一个 OperationCanceledException 异常。
'CORRECTED VERSION OF LAST FUNCTION IN VISUAL BASIC BY GLENNG
Protected Overrides Function GetWebRequest(ByVal address As System.Uri) As System.Net.WebRequest
Dim w As System.Net.WebRequest = MyBase.GetWebRequest(address)
If _TimeoutMS <> 0 Then
w.Timeout = _TimeoutMS
End If
Return w '<<< NOTICE: MyBase.GetWebRequest(address) DOES NOT WORK >>>
End Function
internal class WebConnection : WebClient
{
internal int Timeout { get; set; }
protected override WebRequest GetWebRequest(Uri Address)
{
WebRequest WebReq = base.GetWebRequest(Address);
WebReq.Timeout = Timeout * 1000 // Seconds
return WebReq;
}
}
private async Task GetDataAsyncWithTimeout()
{
await Task.Run(() =>
{
using (WebConnection webClient = new WebConnection())
{
webClient.Timeout = 5; // Five seconds (the multiplication is in the override)
webClient.DownloadData("https://www.yourwebsite.com");
}
});
} // await GetDataAsyncWithTimeout()
private void GetDataSyncWithTimeout()
{
using (WebConnection webClient = new WebConnection())
{
webClient.Timeout = 5; // Five seconds (the multiplication is in the override)
webClient.DownloadData("https://www.yourwebsite.com");
}
} // GetDataSyncWithTimeout()