c#之在 "await DownloadTaskAsync"上调用 WebClient.CancelAsync 时出现 WebException

这很好用:

private WebClient _webClient; 
 
private void ButtonStart_Click(object sender, RoutedEventArgs e) { 
    using (_webClient = new WebClient()) { 
        _webClient.DownloadFileTaskAsync("https://speed.hetzner.de/100MB.bin", @"D:\100MB.bin"); 
    } 
} 
 
private void ButtonStop_Click(object sender, RoutedEventArgs e) { 
    _webClient.CancelAsync(); 
} 

虽然这段代码(注意异步/等待模式)...:

private WebClient _webClient; 
 
private async void ButtonStart_Click(object sender, RoutedEventArgs e) { 
    using (_webClient = new WebClient()) { 
        await _webClient.DownloadFileTaskAsync("https://speed.hetzner.de/100MB.bin", @"D:\100MB.bin"); 
    } 
} 
 
private void ButtonStop_Click(object sender, RoutedEventArgs e) { 
    _webClient.CancelAsync(); 
} 

...抛出以下异常:

System.Net.WebException

The request was aborted: The request was canceled.

   at System.Net.ConnectStream.EndRead(IAsyncResult asyncResult) 
   at System.Net.WebClient.DownloadBitsReadCallbackState(DownloadBitsState state, IAsyncResult result) 
--- End of stack trace from previous location where exception was thrown --- 
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) 
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) 
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult() 
   at WpfApp1.MainWindow.<ButtonStart_Click>d__2.MoveNext() in WpfApp1\MainWindow.xaml.cs:line 19 

如何在不引发异常的情况下取消以 await WebClient.DownloadFileTaskAsync() 开始的任务？

请您参考如下方法:

异常(exception)正是它应该的工作方式。

如果您不希望该异常从您的事件处理程序传播出去，则捕获该异常。