c# - 如何使用 IAsyncResult 从 WCF 异步中的回调中抛出异常

Question

我在我的项目中使用 WCF 异步调用，并且我使用的是客户端异步方法。我有一个像下面这样的场景 -

  //Code in Business Layer and this method is called from Web layer 
    private void GetGeneralNews()
    {
        client.BeginGetGeneralNewsFeed(GeneralNewsCallback, null);
    }

    //Call Back Method
    private static void GeneralNewsCallback(IAsyncResult asyncResult)
    {
       string response = string.Empty;

       try
       {
          response = client.EndGetGeneralNewsFeed(asyncResult);
       }
       catch(Exception ex)
       {
          throw ex; // Here is the problem. It does not throw the exception to the web layer instead it will suppress the   error.
       }
    }

因此，如上面的代码片段所示，它不会将异常从业务层抛出到 Web 层，因为它会在业务层本身中被抑制。

我查看了一些他们建议采用异步和等待方法的博客和网站，因为我有 .NET 4.0 框架并且我看到“生成基于任务的操作”选项被禁用.因此，如果有任何使用“IAsyncResult”(在客户端开始和结束)的选项，请告诉我。如果还有其他方法也欢迎。

请有人帮助我。

谢谢。

Answer 1

这是一个示例应用程序，它显示 WCF 不会吞噬异常。如果您没有收到异常，则它必须被您的服务器端代码吞没。

using System;
using System.ServiceModel;
using System.ServiceModel.Description;
using WcfQ.QServiceReference;

namespace WcfQ
{
[ServiceBehavior(IncludeExceptionDetailInFaults = true)]
public class QService : IQService
{
    public void Foo()
    {
        throw new ApplicationException("Please catch this");
    }
}

[ServiceContract]
public interface IQService
{
    [OperationContract]
    void Foo();
}

class Program
{
    static private QServiceClient client;

    static void Main(string[] args)
    {
        ServiceHost host = new ServiceHost(typeof(QService), new Uri("http://localhost:20001/q"));
        AddWsdlSupport(host);
        host.AddServiceEndpoint(typeof (IQService), new WSHttpBinding(SecurityMode.None), "");
        host.Open();

        client = new QServiceClient();
        client.BeginFoo(FooCallback, null);
        Console.WriteLine("ready");
        Console.ReadKey();
    }

    private static void FooCallback(IAsyncResult asyncResult)
    {
        try
        {
            client.EndFoo(asyncResult);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Got the exception: " + ex.Message);
        }
    }

    static void AddWsdlSupport(ServiceHost svcHost)
    {
        ServiceMetadataBehavior smb = svcHost.Description.Behaviors.Find<ServiceMetadataBehavior>();
        // If not, add one
        if (smb == null)
            smb = new ServiceMetadataBehavior();
        smb.HttpGetEnabled = true;
        smb.MetadataExporter.PolicyVersion = PolicyVersion.Policy15;
        svcHost.Description.Behaviors.Add(smb);
        // Add MEX endpoint
        svcHost.AddServiceEndpoint(
          ServiceMetadataBehavior.MexContractName,
          MetadataExchangeBindings.CreateMexHttpBinding(),
          "mex"
        );

    }
}

这是这个程序的输出:

ready 
Got the exception: Please catch this