c# - 如何为 WebClient.DownloadFileAsync 捕获 404 WebException

Question

这段代码:

try
{
  _wcl.DownloadFile(url, currentFileName);
}
catch (WebException ex)
{
  if (ex.Status == WebExceptionStatus.ProtocolError && ex.Response != null)
    if ((ex.Response as HttpWebResponse).StatusCode == HttpStatusCode.NotFound)
      Console.WriteLine("\r{0} not found.     ", currentFileName);
}

下载文件并通知是否发生 404 错误。

我决定异步下载文件:

try
{
  _wcl.DownloadFileAsync(new Uri(url), currentFileName);
}
catch (WebException ex)
{
  if (ex.Status == WebExceptionStatus.ProtocolError && ex.Response != null)
    if ((ex.Response as HttpWebResponse).StatusCode == HttpStatusCode.NotFound)
      Console.WriteLine("\r{0} not found.     ", currentFileName);
}

现在，如果服务器返回 404 错误并且 WebClient 生成一个空文件，则不会触发此 catch block 。

Answer 1

您需要处理 DownloadFileCompleted事件并检查 AsyncCompletedEventArgs 的 Error 属性.

链接中有很好的示例。