Dependency injection in ASP.NET Core
ASP.NET Core contains a built-in dependency injection mechanism. In the Startup.cs file, there is a method called ConfigureServices which registers all application services in the IServiceCollection parameter.
The collection is managed by the Microsoft.Extensions.DependencyInjection library. It provides basic functionality for dependency injection, there is a lot of extensions (like Scrutor) for convention-based registrations, and it is possible to integrate it with other popular dependency injection containers like Autofac.
When you call app.UseDotVVM<DotvvmStartup>(...), it registers several internal services which DotVVM uses the IServiceCollection, for example the view compiler, viewmodel serializer, and so on.
It also invokes the ConfigureServices method in the DotvvmStartup class, which you can use to register DotVVM-related dependencies, such as control libraries (DotVVM Business Pack), file upload service, and others.
Register services
To register services unrelated to DotVVM infrastructure, you can just call one of the following methods:
public void ConfigureServices(IServiceCollection services)
{
...
services.AddSingleton<ICustomService, CustomService>();
services.AddTransient<ICustomService2, CustomService2>();
services.AddScoped<ICustomService3, CustomService3>();
}
To register DotVVM-related services (IUploadedFileStorage for example), use the ConfigureServices method in DotvvmStartup:
public void ConfigureServices(IDotvvmServiceCollection options)
{
options.AddTempFileStorages("Temp");
}
DotVVM will be able to inject these services if they are specified as parameters of the viewmodel constructor.
Alternative containers
Optionally, the ConfigureServices method can return its own IServiceProvider which will be used instead of the default one. This is useful if you want to use an alternative container.
For example, the default Microsoft.Extensions.DependencyInjection library doesn't support advanced scenarios like registering services by conventions or working with open generic types. This can be a reason to use an alternative dependency injection container.
Autofac is one of the popular DI containers which works with ASP.NET Core. You can use this code to use Autofac:
public IServiceProvider ConfigureServices(IServiceCollection services)
{
...
// create the Autofac container builder
var builder = new ContainerBuilder();
// find all modules with container configuration in current assembly
builder.RegisterAssemblyModules(typeof(Startup).GetTypeInfo().Assembly);
// combine the rules with the services already registered in the IServiceCollection
builder.Populate(services);
// create and return the container
var applicationContainer = builder.Build();
return new AutofacServiceProvider(applicationContainer);
}