Scrutor

Scrutor - I search or examine thoroughly; I probe, investigate or scrutinize
From scrūta, as the original sense of the verb was to search through trash. - https://en.wiktionary.org/wiki/scrutor

Assembly scanning and decoration extensions for Microsoft.Extensions.DependencyInjection

Installation

Install the Scrutor NuGet Package.

Package Manager Console

Install-Package Scrutor

.NET Core CLI

dotnet add package Scrutor

Usage

The library adds two extension methods to IServiceCollection:

• Scan - This is the entry point to set up your assembly scanning.
• Decorate - This method is used to decorate already registered services.

See Examples below for usage examples.

Examples

Scanning

var collection = new ServiceCollection();

collection.Scan(scan => scan
     // We start out with all types in the assembly of ITransientService
    .FromAssemblyOf<ITransientService>()
        // AddClasses starts out with all public, non-abstract types in this assembly.
        // These types are then filtered by the delegate passed to the method.
        // In this case, we filter out only the classes that are assignable to ITransientService.
        .AddClasses(classes => classes.AssignableTo<ITransientService>())
            // We then specify what type we want to register these classes as.
            // In this case, we want to register the types as all of its implemented interfaces.
            // So if a type implements 3 interfaces; A, B, C, we'd end up with three separate registrations.
            .AsImplementedInterfaces()
            // And lastly, we specify the lifetime of these registrations.
            .WithTransientLifetime()
        // Here we start again, with a new full set of classes from the assembly above.
        // This time, filtering out only the classes assignable to IScopedService.
        .AddClasses(classes => classes.AssignableTo<IScopedService>())
            // Now, we just want to register these types as a single interface, IScopedService.
            .As<IScopedService>()
            // And again, just specify the lifetime.
            .WithScopedLifetime()
        // Generic interfaces are also supported too, e.g. public interface IOpenGeneric<T> 
        .AddClasses(classes => classes.AssignableTo(typeof(IOpenGeneric<>)))
            .AsImplementedInterfaces()
        // And you scan generics with multiple type parameters too
        // e.g. public interface IQueryHandler<TQuery, TResult>
        .AddClasses(classes => classes.AssignableTo(typeof(IQueryHandler<,>)))
            .AsImplementedInterfaces());

Scanning compiled view (UI) types

By default, Scrutor excludes compiler-generated types from the .AddClasses() type filters. When loading views from a framework such as Avalonia UI, we need to opt in to compiler-generated types, like this:

.AddClasses(classes => classes
    // Opt-in to compiler-generated types
    .WithAttribute<CompilerGeneratedAttribute>()
    // Optionally filter types to reduce number of service registrations.
    .InNamespaces("MyApp.Desktop.Views")
    .AssignableToAny(
        typeof(Window),
        typeof(UserControl)
    )
    .AsSelf()
    .WithSingletonLifetime()

With some UI frameworks, these compiler-generated views implement quite a few interfaces, so unless you need them, it's probably best to register these classes .AsSelf(); in other words, be very precise with your filters that accept compiler generated types.

Decoration

var collection = new ServiceCollection();

// First, add our service to the collection.
collection.AddSingleton<IDecoratedService, Decorated>();

// Then, decorate Decorated with the Decorator type.
collection.Decorate<IDecoratedService, Decorator>();

// Finally, decorate Decorator with the OtherDecorator type.
// As you can see, OtherDecorator requires a separate service, IService. We can get that from the provider argument.
collection.Decorate<IDecoratedService>((inner, provider) => new OtherDecorator(inner, provider.GetRequiredService<IService>()));

var serviceProvider = collection.BuildServiceProvider();

// When we resolve the IDecoratedService service, we'll get the following structure:
// OtherDecorator -> Decorator -> Decorated
var instance = serviceProvider.GetRequiredService<IDecoratedService>();