Handle FTP client.DownloadString文件未找到异常[重复]

这是我为自己创建的一个方法,它看起来像是在做你正在寻找的事情。

   private bool FileExists(string url, out int contentLength)
    {
        bool fileExistsAnswer;
        try 
        {
            WebRequest request = HttpWebRequest.Create(url);
            request.Method = "HEAD"; // Just get the document headers, not the data.    
            request.Credentials = System.Net.CredentialCache.DefaultCredentials;    // This may throw a WebException:    
            using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
            {
                if (response.StatusCode == HttpStatusCode.OK)
                {
                    fileExistsAnswer = true;
                    contentLength = Convert.ToInt32(response.ContentLength);
                }
                else
                {
                    fileExistsAnswer = false;
                    contentLength = 0;
                }
            }            
        }
        catch(Exception Ex)
        {
            fileExistsAnswer = false;
            contentLength = 0;
        }

        return fileExistsAnswer;

    } // private bool FileExists(string url)

我就是这样用的。

            string productThumbUrl = string.Empty;
            int contentLength;
            if (FileExists(productThumbUrl_png, out contentLength))
            {
                productThumbUrl = productThumbUrl_png;
            }