How to create dependency injection for ASP.NET MVC

Question

Creating Dependency Injection with ASP.NET Core is fairly easy. The documentation explains it very well here and this guy has a killer video to explain it.

However, I want to do the same thing with my ASP.NET MVC 5 project. How can handle dependency injection with ASP.MVC 5?

Also, is Dependency injection limited to controllers only or can it work with any class?

Answer 1

In ASP.Net MVC you can use the .Net Core DI from NuGet rather than one of the third-party alternatives:-

using Microsoft.Extensions.DependencyInjection

For the MVC Start/Configuration class:-

public void Configuration(IAppBuilder app)
        {
            // We will use Dependency Injection for all controllers and other classes, so we'll need a service collection
            var services = new ServiceCollection();

            // configure all of the services required for DI
            ConfigureServices(services);

            // Configure authentication
            ConfigureAuth(app);

            // Create a new resolver from our own default implementation
            var resolver = new DefaultDependencyResolver(services.BuildServiceProvider());

            // Set the application resolver to our default resolver. This comes from "System.Web.Mvc"
            //Other services may be added elsewhere through time
            DependencyResolver.SetResolver(resolver);
        }

My project uses Identity User and I've replaced the OWIN start-up configuration to follow a service-based approach instead. The default Identity User classes use static factory methods to create instances. I've moved that code into the constructors and relied on DI to provide the appropriate injection. It is still work in progress but here is where I am at:-

 public void ConfigureServices(IServiceCollection services)
        {               
            //====================================================
            // Create the DB context for the IDENTITY database
            //====================================================
            // Add a database context - this can be instantiated with no parameters
            services.AddTransient(typeof(ApplicationDbContext));

            //====================================================
            // ApplicationUserManager
            //====================================================
            // instantiation requires the following instance of the Identity database
            services.AddTransient(typeof(IUserStore<ApplicationUser>), p => new UserStore<ApplicationUser>(new ApplicationDbContext()));

            // with the above defined, we can add the user manager class as a type
            services.AddTransient(typeof(ApplicationUserManager));

            //====================================================
            // ApplicationSignInManager
            //====================================================
            // instantiation requires two parameters, [ApplicationUserManager] (defined above) and [IAuthenticationManager]
            services.AddTransient(typeof(Microsoft.Owin.Security.IAuthenticationManager), p => new OwinContext().Authentication);
            services.AddTransient(typeof(ApplicationSignInManager));

            //====================================================
            // ApplicationRoleManager
            //====================================================
            // Maps the rolemanager of identity role to the concrete role manager type
            services.AddTransient<RoleManager<IdentityRole>, ApplicationRoleManager>();

            // Maps the role store role to the implemented type
            services.AddTransient<IRoleStore<IdentityRole, string>, RoleStore<IdentityRole>>();
            services.AddTransient(typeof(ApplicationRoleManager));

            //====================================================
            // Add all controllers as services
            //====================================================
            services.AddControllersAsServices(typeof(Startup).Assembly.GetExportedTypes()
                .Where(t => !t.IsAbstract && !t.IsGenericTypeDefinition)
            .Where(t => typeof(IController).IsAssignableFrom(t)
            || t.Name.EndsWith("Controller", StringComparison.OrdinalIgnoreCase)));
        }

The Account Controller class has the single constructor:-

[Authorize]
public class AccountController : Controller
{
    private ApplicationSignInManager _signInManager;
    private ApplicationUserManager _userManager;
    private RoleManager<IdentityRole> _roleManager;

    public AccountController(ApplicationUserManager userManager, ApplicationSignInManager signInManager, RoleManager<IdentityRole> roleManager)
    {
        UserManager = userManager;
        SignInManager = signInManager;
        RoleManager = roleManager;
    }