使用Visual Studio 2017进行调试时，“请求在此上下文中不可用”

Question

I upgraded from Visual Studio 2015 to Visual Studio 2017. The following code runs when it is deployed to Azure App Services and when I debug it with Visual Studio 2015. But when debugging in Visual Studio 2017, it throws the exception:

Request is not available in this context

For VS2015 and VS2017 IIS Express is used for debugging. Now with VS2017 IIS 10.0 Express (10.0.1737) is installed, I do not remember which version was used with VS2015.

The code is C# based on the ASP.NET 4.5.2 Azure API App template. It registers a receiver for subscribing events from Azure Event Hub.

using System;
using System.Web.Http;
using System.Web.Http.Cors;
using System.Configuration;
using Microsoft.Azure.EventHubs;
using Microsoft.Azure.EventHubs.Processor;
using Microsoft.ApplicationInsights;
using System.Collections.Generic;

namespace ....

public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services
            config.EnableCors();
            // Web API routes
            config.MapHttpAttributeRoutes();

            try
            {
                Console.WriteLine("Registering EventProcessor...");

                ...

                var eventProcessorHost = new EventProcessorHost(
                        EhEntityPath,
                        EhConsumerGroup,
                        EhConnectionString,
                        StorageConnectionString,
                        StorageContainerName
                        );

                // Registers the Event Processor Host and starts receiving messages
                eventProcessorHost.RegisterEventProcessorAsync<Helper.EventProcessor>(); 
            }
            catch (Exception ex)
...

The exception is thrown at the line

eventProcessorHost.RegisterEventProcessorAsync<Helper.EventProcessor>(); 

But this issue seems not to be related to Azure Event Hub. Because I get this exception also in global.asax.cs when trying to create an Application Insights event:

new TelemetryClient().TrackEvent("Application started");

I know there are some other posts regarding the exception "Request is not available in this context" but this seems to be a special behavior of VS2017.

My local environment is:

Microsoft Visual Studio Enterprise 2017 
Version 15.2 (26430.16) Release
VisualStudio.15.Release/15.2.0+26430.16
Microsoft .NET Framework
Version 4.7.02046

Installed Version: Enterprise

Visual C# 2017   00369-60000-00001-AA377
Microsoft Visual C# 2017

Application Insights Tools for Visual Studio Package   8.6.00404.2
Application Insights Tools for Visual Studio

ASP.NET and Web Tools 2017   15.0.30503.0
ASP.NET and Web Tools 2017

ASP.NET Web Frameworks and Tools 2017   5.2.50303.0

Azure App Service Tools v3.0.0   15.0.30209.0
Azure App Service Tools v3.0.0

Common Azure Tools   1.9

Answer 1

According to your description, I created the ASP.NET 4.5.2 Azure API App application on my side and debugged it on VS2015 (Enterprise, Version 14.0.25431.01 Update 3) and VS2017 (Enterprise Preview, Version 15.3.0 Preview 7.1) with IIS Express (10.0.14358.100), both could debug successfully and the custom events and metrics could be sent to my application insights.

Based on your issue, I would suggest you starting your application via VS without debugging to narrow this issue or you could use the cmd.exe and run iisexpress /path:"c:\\myapp\\" /port:80 to check whether your application could work as expected.

Answer 2

I deinstalled VS2017 with all components and reinstalled the latest Version 15.3.3. Now the code runs. No idea what went wrong with the first installation.