谁能用示例客户端应用程序解释 IExceptionHandler 的工作流程

我在此示例中面临以下问题：

我找不到IsOutermostCatchBlock in ExceptionContext

如果发生异常，则此HandleAsync方法执行了两次。

(http://www.asp.net/web-api/overview/web-api-routing-and-actions/web-api-global-error-handling http://www.asp.net/web-api/overview/web-api-routing-and-actions/web-api-global-error-handling)

public class CustomExceptionHandler : IExceptionHandler
{
    public virtual Task HandleAsync(ExceptionHandlerContext context,
                                        CancellationToken cancellationToken)
    {
        if (!ShouldHandle(context))
        {
            return Task.FromResult(0);
        }

            return HandleAsyncCore(context, cancellationToken);
        }

        public virtual Task HandleAsyncCore(ExceptionHandlerContext context,
                                            CancellationToken cancellationToken)
        {
            HandleCore(context);
            return Task.FromResult(0);
        }

        public virtual void HandleCore(ExceptionHandlerContext context)
        {
        }

        public virtual bool ShouldHandle(ExceptionHandlerContext context)
        {    
             return context.ExceptionContext.IsOutermostCatchBlock;
        }

    }

    public class OopsExceptionHandler : CustomExceptionHandler
    {
        public override void HandleCore(ExceptionHandlerContext context)
        {
            context.Result = new TextPlainErrorResult
            {
                Request = context.ExceptionContext.Request,
                Content = "Oops! Sorry! Something went wrong." +
                          "Please contact [email protected] /cdn-cgi/l/email-protection so we can try to fix it."
            };
        }

        private class TextPlainErrorResult : IHttpActionResult
        {
            public HttpRequestMessage Request { get; set; }
            public string Content { get; set; }

            public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
            {
                HttpResponseMessage response =
                                 new HttpResponseMessage(HttpStatusCode.InternalServerError);
                response.Content = new StringContent(Content);
                response.RequestMessage = Request;
                return Task.FromResult(response);
            }
        }
    }
}

CatchBlock.IsTopLevel

IsOutermostCatchBlock不存在。 使用CatchBlock.IsTopLevel反而：

public virtual bool ShouldHandle(ExceptionHandlerContext context)
{
  return context.ExceptionContext.CatchBlock.IsTopLevel;
}

NuDoq 来源：异常处理上下文 http://www.nudoq.org/#!/Packages/Microsoft.AspNet.WebApi.Core/System.Web.Http/ExceptionHandlerContext and 异常上下文捕获块 http://www.nudoq.org/#!/Packages/Microsoft.AspNet.WebApi.Core/System.Web.Http/ExceptionContextCatchBlock