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Running Code at Startup

Autofac provides the ability for components to be notified or automatically activated when the container is built.

There are two automatic activation mechanisms available: - Startable components - Auto-activated components

In both cases, at the time the container is built, the component will be activated.

Startable Components

A startable component is one that is activated by the container when the container is initially built and has a specific method called to bootstrap an action on the component.

The key is to implement the Autofac.IStartable interface. When the container is built, the component will be activated and the IStartable.Start() method will be called.

This only happens once, for a single instance of each component, the first time the container is built. Resolving startable components by hand won't result in their Start() method being called. It isn't recommended that startable components implement other services, or be registered as anything other than SingleInstance().

Components that need to have something like a Start() method called each time they are activated should use :doc:`a lifetime event <events>` like OnActivated instead.

To create a startable component, implement Autofac.IStartable:

public class StartupMessageWriter : IStartable
{
   public void Start()
   {
      Console.WriteLine("App is starting up!");
   }
}

Then register your component and be sure to specify it as IStartable or the action won't be called:

var builder = new ContainerBuilder();
builder
   .RegisterType<StartupMessageWriter>()
   .As<IStartable>()
   .SingleInstance();

When the container is built, the type will be activated and the IStartable.Start() method will be called. In this example, a message will be written to the console.

Auto-Activated Components

An auto-activated component is a component that simply needs to be activated one time when the container is built. This is a "warm start" style of behavior where no method on the component is called and no interface needs to be implemented - a single instance of the component will be resolved with no reference to the instance held.

To register an auto-activated component, use the AutoActivate() registration extension.

var builder = new ContainerBuilder();
builder
   .RegisterType<TypeRequiringWarmStart>()
   .AutoActivate();