ServiceLocatorImplBase.cs not found

Question

When my WebAPI controller is called from a client, I run into the following errors:

ServiceLocatorImplBase.cs not found error

An exception of type 'Microsoft.Practices.ServiceLocation.ActivationException' occurred in Microsoft.Practices.ServiceLocation.dll but was not handled in user code

The WebAPI controllers use constructor injection to inject a repository dependency which should be resolved by StructureMap IoC. Interestingly, the same code runs fine on my another development machine. Here is my stack trace. Thanks for your help.

System.ArgumentNullException was unhandled by user code
HResult=-2147467261
Message=Value cannot be null.
Parameter name: httpContext
Source=System.Web
ParamName=httpContext

StackTrace:

at System.Web.HttpContextWrapper..ctor(HttpContext httpContext)
at WebApi2.DependencyResolution.StructureMapDependencyScope.get_HttpContext() in c:.........\WebApi2\DependencyResolution\StructureMapDependencyScope.cs:line 69
at WebApi2.DependencyResolution.StructureMapDependencyScope.get_CurrentNestedContainer() in c:.........\WebApi2\DependencyResolution\StructureMapDependencyScope.cs:line 55
at WebApi2.DependencyResolution.StructureMapDependencyScope.DisposeNestedContainer() in c:.........\WebApi2\DependencyResolution\StructureMapDependencyScope.cs:line 90
at WebApi2.DependencyResolution.StructureMapDependencyScope.Dispose() in c:.........\WebApi2\DependencyResolution\StructureMapDependencyScope.cs:line 85
at WebApi2.App_Start.StructuremapMvc.End() in c:.........\WebApi2\App_Start\StructuremapMvc.cs:line 44

score 1 · Accepted Answer · edited Jan 30 '18 at 20:18

Thanks for your reply. Both machines are running integrated mode. The error is really misleading and threw me off to a wrong track. I spent hours trying to find where this ServiceLocatorImplBase.cs resides. I happened to look into the deeply nested inner exceptions, and found that the inner most exception (5th level) complains some entities generated by POCO generator have no identity key. This is because I manually added the foreign key relationship among some entities with

public virtual RelatedEntity1 {get;set;}
public virtual RelatedEntity2 {get;set;}

without setting [key] attributes in the related entities. I am not sure if this can be fixed but the exception message should not lead people to the wrong track.

score 0 · Answer 2 · edited May 23 '17 at 11:44

The problem you are running into is because you are attempting to resolve HttpContext at the point in time that the application is composed (typically done in the Application_Start event of Global.asax). HttpContext is part of the application's runtime state. It is null at the point in time when the application is being composed.

The reason why it seems to work in your development environment is likely because your development environment's application pool is running in classic mode. Most likely the other environments are (correctly) running in integrated mode. So, this is a design issue, not a problem with deployment as you might expect.

The solution is to use an Abstract Factory so you can defer instantiating of the HttpContextWrapper until runtime. Then you can inject the abstract factory rather than HttpContextWrapper into your services.

public interface IHttpContextFactory
{
    HttpContextBase Create();
}

public class HttpContextFactory
    : IHttpContextFactory
{
    public HttpContextBase Create()
    {
        return new HttpContextWrapper(HttpContext.Current);
    }
}

See this answer and this answer for a complete examples including usage.

ServiceLocatorImplBase.cs not found

2 Answers2