可能的身份验证问题？在 Silverlight 4 中通过 WebClient 加载 JSON

Question

我正在使用 Silverlight 4，当我的页面加载时，我会调用

beginGet("my/people/", new OpenReadCompletedEventHandler(continueLoadStamData));

我定义为

private void beginGet(string endpoint, OpenReadCompletedEventHandler callback)
{
  WebClient wc = new WebClient();
  wc.Credentials = new NetworkCredential(username, password);
  wc.OpenReadCompleted += callback;
  wc.OpenReadAsync(new Uri(baseURL + endpoint));
}

然后继续LoadStamData()

void continueLoadStamData(object sender, OpenReadCompletedEventArgs e)
{
  JsonObject root = (JsonObject)JsonObject.Load(e.Result);
}

我的问题是，当我到达 e.Result 时，它会引发异常。这与我尝试使用 WebRequest req = ...; req.Credentials = new NetworkCredential(username, password) 时遇到的异常相同：

{System.Reflection.TargetInvocationException: An exception occurred during the operation, making the result invalid.  Check InnerException for exception details. ---> System.Net.WebException: An exception occurred during a WebClient request. ---> System.NotImplementedException: This property is not implemented by this class.
   at System.Net.WebRequest.set_Credentials(ICredentials value)
   at System.Net.WebClient.GetWebRequest(Uri address)
   at System.Net.WebClient.OpenReadAsync(Uri address, Object userToken)
   --- End of inner exception stack trace ---
   --- End of inner exception stack trace ---
   at System.ComponentModel.AsyncCompletedEventArgs.RaiseExceptionIfNecessary()
   at System.Net.OpenReadCompletedEventArgs.get_Result()
   at JSONSample.MainPage.continueLoadStamData(Object sender, OpenReadCompletedEventArgs e)
   at System.Net.WebClient.OnOpenReadCompleted(OpenReadCompletedEventArgs e)
   at System.Net.WebClient.OpenReadOperationCompleted(Object arg)}

您知道发生了什么吗？如何确保基本身份验证已实施并让我的请求继续执行？

干杯

尼克

Answer 1

基于Mark Monster's post here，您的 beginGet 方法中缺少一些代码行。它应该是这样的：

private void beginGet(string endpoint, OpenReadCompletedEventHandler callback)
{
  WebRequest.RegisterPrefix("http://", System.Net.Browser.WebRequestCreator.ClientHttp);  
  WebClient wc = new WebClient();  
  wc.Credentials = new NetworkCredential(username, password);
  wc.UseDefaultCredentials = false; 
  wc.OpenReadCompleted += callback;  
  wc.OpenReadAsync(new Uri(baseURL + endpoint));
}

另外，如果您只是想从服务器获取 JSON，您应该能够使用 DownloadStringAsync 而不是 OpenReadAsync，这可能会简化事情。