How does UnityWebActivator.start() get called in asp.net app

Question

I am trying to understand how Unity IoC works in my Web application. I have created a mvc&api application using visual studio 2015 project template.

Using NuGet i installed Unity. Modified the Unity config to register the types i wanted injected. I had originally added UnityWebActivator.start() to my global.asax file thinking it had to be there in the startup, but when i comment it out, everything still works.

How does the UnityWebActivator get called to configure the new IoC container for unity?

using System.Linq;
using System.Web.Mvc;
using Microsoft.Practices.Unity.Mvc;

[assembly: WebActivatorEx.PreApplicationStartMethod(typeof(WebDirectory.App_Start.UnityWebActivator), "Start")]
[assembly: WebActivatorEx.ApplicationShutdownMethod(typeof(WebDirectory.App_Start.UnityWebActivator), "Shutdown")]

namespace WebDirectory.App_Start
{
/// <summary>Provides the bootstrapping for integrating Unity with ASP.NET MVC.</summary>
public static class UnityWebActivator
{
    /// <summary>Integrates Unity when the application starts.</summary>
    public static void Start() 
    {
        var container = UnityConfig.GetConfiguredContainer();

        FilterProviders.Providers.Remove(FilterProviders.Providers.OfType<FilterAttributeFilterProvider>().First());
        FilterProviders.Providers.Add(new UnityFilterAttributeFilterProvider(container));

        DependencyResolver.SetResolver(new UnityDependencyResolver(container));

        // TODO: Uncomment if you want to use PerRequestLifetimeManager
        // Microsoft.Web.Infrastructure.DynamicModuleHelper.DynamicModuleUtility.RegisterModule(typeof(UnityPerRequestHttpModule));
    }

    /// <summary>Disposes the Unity container when the application is shut down.</summary>
    public static void Shutdown()
    {
        var container = UnityConfig.GetConfiguredContainer();
        container.Dispose();
    }
}
}

Answer 1

The WebActivatorEx.PreApplicationStartMethod calls the start method early on during application initialization. You'll notice there's also a shutdown method that is called when the application ends.