從網站下載.pdf文件。文件損壞

Question

我想下載下面的PDF文件（該文件點擊它後幾秒鐘內產生的）：

PDF Link

我嘗試下面的代碼來做到這一點：

static void DownloadByWebClient() 
{ 
    string url = "http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=NL&language=EN-generic&productNumber=271004&brand=SIAL&PageToGoToURL=null"; 
    string clientfile = @"C:\Users\Test\Downloads\newfile.pdf"; 

    WebClient wc = new WebClient(); 
    wc.UseDefaultCredentials = true; 
    wc.Credentials = CredentialCache.DefaultCredentials; 

    wc.DownloadFileAsync(new Uri(url, UriKind.Absolute), clientfile); 
} 

pdf文件已創建。但是，當我嘗試打開它時，我收到一條消息說它已損壞。 也許問題在於文件在可以下載之前首先生成？

我也試過DownloadFile方法。但後來引發錯誤：

A first chance exception of type 'System.Net.WebException' occurred in System.dll 
System.Net.WebException: An exception occurred during a WebClient request. 
System.Configuration.ConfigurationErrorsException: 
Error creating the Web Proxy specified in the 'system.net/defaultProxy' configuration section. 
---> System.Net.Sockets.SocketException: An invalid argument was supplied 
at System.Net.SafeCloseSocketAndEvent.CreateWSASocketWithEvent(AddressFamily addressFamily, 
SocketType socketType, ProtocolType protocolType, Boolean autoReset, Boolean signaled) 
at System.Net.NetworkAddressChangePolled..ctor() 
at System.Net.AutoWebProxyScriptEngine.AutoDetector.Initialize() 
at System.Net.AutoWebProxyScriptEngine.AutoDetector.get_CurrentAutoDetector() 
at System.Net.AutoWebProxyScriptEngine..ctor(WebProxy proxy, Boolean useRegistry) 
at System.Net.WebProxy.UnsafeUpdateFromRegistry() 
at System.Net.WebProxy..ctor(Boolean enableAutoproxy) 
at System.Net.Configuration.DefaultProxySectionInternal..ctor(DefaultProxySection section) 
at System.Net.Configuration.DefaultProxySectionInternal.GetSection() 
--- End of inner exception stack trace --- 

at System.Net.Configuration.DefaultProxySectionInternal.GetSection() 
at System.Net.WebRequest.get_InternalDefaultWebProxy() 
at System.Net.HttpWebRequest..ctor(Uri uri, ServicePoint servicePoint) 
at System.Net.HttpRequestCreator.Create(Uri Uri) 
at System.Net.WebRequest.Create(Uri requestUri, Boolean useUriBase) 
at System.Net.WebRequest.Create(Uri requestUri) 
at System.Net.WebClient.GetWebRequest(Uri address) 
at System.Net.WebClient.DownloadFile(Uri address, String fileName) 
--- End of inner exception stack trace --- 
at System.Net.WebClient.DownloadFile(Uri address, String fileName) 
--- End of inner exception stack trace --- 

可能是什麼原因？

在此先感謝！

Answer 1

我根據OP的評論和我的測試改變了我的答案。 我可以運行下面的代碼，它工作得很好。該文件被下載，並在我的本地磁盤上的PDF是好的。

public void DLTest() 
{ 
    string url = "https://www.osha.gov/Publications/Abate/abate.pdf"; 
    string clientfile = @"C:\Test\newfile3.pdf"; 

    WebClient wc = new WebClient(); 

    wc.DownloadFile(new Uri(url, UriKind.Absolute), clientfile); 
} 

然而，當我用你的網址「http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=NL&language=EN-generic&productNumber=271004&brand=SIAL&PageToGoToURL=null」的PDF格式不包含數據。看來您使用的網址不支持以PDF形式下載此信息。

您可以嘗試從不同站點下載MSDS，例如下面的代碼使用不同的URL。

public void DLTest() 
{ 
    string url = "http://www.sciencelab.com/msds.php?msdsId=9927335"; 
    string clientfile = @"C:\Test\newfile.pdf"; 

    WebClient wc = new WebClient(); 

    wc.DownloadFile(new Uri(url, UriKind.Absolute), clientfile); 
}