c# - 如何检查 WebClient 请求是否有 404 错误

Question

我正在编写一个下载到文件的程序。第二个文件不是必需的，只是在某些时候包含在内。如果不包含第二个文件，它将返回一个 HTTP 404 错误。

现在，问题是当返回这个错误时，它结束了整个程序。我想要的是继续程序并忽略 HTTP 错误。所以，我的问题是如何从 WebClient.DownloadFile 请求中捕获 HTTP 404 错误？

这是当前使用的代码::

WebClient downloader = new WebClient();
foreach (string[] i in textList)
{
    String[] fileInfo = i;
    string videoName = fileInfo[0];
    string videoDesc = fileInfo[1];
    string videoAddress = fileInfo[2];
    string imgAddress = fileInfo[3];
    string source = fileInfo[5];
    string folder = folderBuilder(path, videoName);
    string infoFile = folder + '\\' + removeFileType(retrieveFileName(videoAddress)) + @".txt";
    string videoPath = folder + '\\' + retrieveFileName(videoAddress);
    string imgPath = folder + '\\' + retrieveFileName(imgAddress);
    System.IO.Directory.CreateDirectory(folder);
    buildInfo(videoName, videoDesc, source, infoFile);
    textBox1.Text = textBox1.Text + @"begining download of files for" + videoName;
    downloader.DownloadFile(videoAddress, videoPath);
    textBox1.Text = textBox1.Text + @"Complete video for" + videoName;
    downloader.DownloadFile(imgAddress, imgPath);
    textBox1.Text = textBox1.Text + @"Complete img for" + videoName;
}

Answer 1

如果您特别想要捕获错误 404:

using (var client = new WebClient())
{
  try
  {
    client.DownloadFile(url, destination);
  }
  catch (WebException wex)
  {
    if (((HttpWebResponse) wex.Response).StatusCode == HttpStatusCode.NotFound)
    {
      // error 404, do what you need to do
    }
  }
}

或者，使用 C# 7 或更高版本:

using (var client = new WebClient())
{
  try
  {
    client.DownloadFile(url, destination);
  }
  catch (WebException ex) when
        (ex.Response is HttpWebResponse wr && wr.StatusCode == HttpStatusCode.NotFound)
  {      
    // error 404, do what you need to do
  }
}