WCF 和 ASP.NET - Server.Execute 抛出对象引用未设置为对象的实例

Question

我有一个调用 WCF 服务的 ASP.NET 页面。此 WCF 服务使用 BackgroundWorker 在我的服务器上异步创建 ASP.NET 页面。奇怪的是，当我执行

WCF 服务

[OperationContract]
[WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.WrappedRequest, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json)]
public void PostRequest(string comments)
{
   // Do stuff


   // If everything went o.k. asynchronously render a page on the server. I do not want to
   // block the caller while this is occurring. 
   BackgroundWorker myWorker = new BackgroundWorker();
   myWorker.DoWork += new DoWorkEventHandler(myWorker_DoWork);
   myWorker.RunWorkerAsync(HttpContext.Current);
}

private void myWorker_DoWork(object sender, DoWorkEventArgs e)
{
  // Set the current context so we can render the page via Server.Execute
  HttpContext context = (HttpContext)(e.Argument);
  HttpContext.Current = context;

  // Retrieve the url to the page
  string applicationPath = context.Request.ApplicationPath;
  string sourceUrl = applicationPath + "/log.aspx";
  string targetDirectory = currentContext.Server.MapPath("/logs/");

  // Execute the other page and load its contents
  using (StringWriter stringWriter = new StringWriter())
  {
    // Write the contents out to the target url
    // NOTE: THIS IS WHERE MY ERROR OCCURS
    currentContext.Server.Execute(sourceUrl, stringWriter);

    // Prepare to write out the result of the log
    targetPath = targetDirectory + "/" + DateTime.Now.ToShortDateString() + ".aspx";
    using (StreamWriter streamWriter = new StreamWriter(targetPath, false))
    {
      // Write out the content to the file
      sb.Append(stringWriter.ToString());
      streamWriter.Write(sb.ToString());
    }
  }
}

奇怪的是，在执行 currentContext.Server.Execute 方法时，它会抛出“对象引用未设置为对象的实例”错误。之所以如此奇怪，是因为我可以在监视窗口中查看 currentContext 属性。此外，Server 不为空。因此，我不知道这个错误是从哪里来的。

有人能指出造成这种情况的正确方向吗？

谢谢！

Answer 1

您正在使用HttpContext - 通常默认情况下不可用于 WCF（并且将是 null） - 毕竟，WCF 可以在 IIS 之外自托管，并且ASP.NET 管道。

如果您需要并且想要使用 HttpContext，您需要明确允许并打开它。在您的服务器配置中，您需要：

<system.serviceModel>        
    <serviceHostingEnvironment aspNetCompatibilityEnabled=”true” />    
</system.serviceModel>

你的服务类也应该用：

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]
public class YourServiceImplementation : IYourService
......

看看

• MSDN: hosting WCF services side-by-side with ASP.NET
• WCF ASP.NET Compatibility Mode

非常广泛地涵盖所有细节。