Creating the bootstrapper

The bootstrapper's responsibility is to initialize Autofac. It is called at the startup of the application. We can create it as follows:

1. In the root of the .NET Standard library project, create a new file called Bootstrapper.cs.
2. Enter the following code:

using Autofac;
using System.Linq;
using System.Reflection;
using Xamarin.Forms;
using DoToo.Views;
using DoToo.Repositories;
using DoToo.ViewModels;

namespace DoToo
{
    public abstract class Bootstrapper
    {
        protected ContainerBuilder ContainerBuilder { get; private 
        set; }
 
        public Bootstrapper()
        {
            Initialize();
            FinishInitialization();
        }
 
        protected virtual void Initialize()
        {
            var currentAssembly = Assembly.GetExecutingAssembly();
            ContainerBuilder = new ContainerBuilder();
 
            foreach (var type in currentAssembly.DefinedTypes
                      .Where(e => 
                             e.IsSubclassOf(typeof(Page)) ||
                             e.IsSubclassOf(typeof(ViewModel)))) 
            {
                ContainerBuilder.RegisterType(type.AsType());
            }
 
            ContainerBuilder.RegisterType<TodoItemRepository>().SingleInstance();
        }
 
        private void FinishInitialization()
        {
            var container = ContainerBuilder.Build();
            Resolver.Initialize(container);
        }
    }
}

The Bootstrapper class is implemented by each platform since this is where the execution of the app begins. This also gives us the option to add platform-specific configurations. To ensure that we inherit from the class, we define it as abstract.

ContainerBuilder is a class defined in Autofac that takes care of creating the container property for us after we finish the configuration. The building of the container property happens in the FinishInitialization method defined at the end and is called by the constructor right after we call the virtual Initialize method. We can override the Initialize method to add custom registrations to each platform.

The Initialize method scans the assembly using reflection for any types that inherit from Page or ViewModel and adds them to the container property. It also adds the TodoItemRepository property as a singleton to the container property. This means that each time we ask for TodoItemRepository, we get the same instance. The default behavior for Autofac (this may vary between libraries) is to give a new instance for each resolution.