我想使用CancellationToken中止文件下载

I want to use the CancellationToken to abort a file download

下载文件是一项I/O操作，.NET平台上提供了异步可取消(基于I/O完成端口)功能.但是您似乎并没有使用它们.

Downloading a file is an I/O operation, for which asynchronous cancelable (I/O completion port based) functions are available on the .NET platform. Yet you seem to not be using them.

相反，您似乎正在使用 Task.Run 创建(一系列)任务，这些任务执行阻止I/O，其中取消令牌没有传递给 Task中的每个任务.运行链.

Instead you appear to be creating (a chain of) tasks using Task.Run that perform blocking I/O, where a cancelation token is not passed on to each task in your Task.Run chain.

有关进行异步，可等待和可取消的文件下载的示例，请参阅:

For examples of doing async, awaitable and cancelable file downloads, refer to:

• 使用 HttpClient :在Windows Phone 8中下载并保存异步文件
• 使用 WebClient :具有自己的取消机制:注册方法:

• Using HttpClient: How to copy HttpContent async and cancelable?
• Windows Phone: Downloading and saving a file Async in Windows Phone 8
• Using WebClient: Has its own cancellation mechanism: the CancelAsync method, you can connect it to your cancellation token, using the token's Register method:

myToken.Register(myWebclient.CancelAsync);

您可以执行以下操作:

static async Task<string> WsGetResponseString(WebRequest webreq, CancellationToken cancelToken)`
{
    cancelToken.Register(webreq.Abort);
    using (var response = await webReq.GetResponseAsync())
    using (var stream = response.GetResponseStream())
    using (var destStream = new MemoryStream())
    {
        await stream.CopyToAsync(destStream, 4096, cancelToken);
        return Encoding.UTF8.GetString(destStream.ToArray());
    }
}