C#网络请求->getresponse强制转换异常，而不是返回状态代码

Question

我正在尝试制作一个图像抓取器，现在对于一些页面，图像没有指定，所以我想根据访问页面时收到的状态码来分析我的输出，但当我试图对我的状态码进行裁剪时，如果找不到页面，我会得到一个异常，而不是状态码，你知道为什么会发生这种情况吗？

if (gameinfo != null)
if (!string.IsNullOrEmpty(gameinfo.image_uri))
try
{
using (System.Net.WebClient client = new System.Net.WebClient())
{
// Build Uri and attempt to fetch a response.
UriBuilder uribuild = new UriBuilder(gameinfo.image_uri);
WebRequest request = WebRequest.Create(uribuild.Uri);
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
switch (response.StatusCode)
{
// Page found and valid entry.
case HttpStatusCode.OK:
using (Stream stream = client.OpenRead(uribuild.Uri))
{
Console.WriteLine(String.Format("Downloading {0}", uribuild.Uri));
System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(stream);
bitmap.Save(System.IO.Path.Combine(rom_root, String.Format("{0}.jpg", file_name.Substring(2).Split('.').First())));
}
break;
// Unspecified status codes.
default:
Console.WriteLine("Unspecified status code found, aborting...");
break;
}
}
} catch(System.Net.WebException ex)
{
// Should be moved to switch with HttpStatusCode.NotFound ^
Console.WriteLine("Image page not found.");
}

Answer 1

GetResponse()实现就是这样。如果响应不是成功的，则抛出WebException。

我同意，我觉得这有点奇怪——如果这至少是一种可选的行为，那就太好了。值得庆幸的是，您可以从正在抛出的WebException中读取状态代码：

....
catch (WebException e)
{
using (WebResponse response = e.Response)
{
HttpWebResponse httpResponse = (HttpWebResponse) response;
var statusCode = httpResponse.StatusCode;
// Do stuff with the statusCode
}
}