J4JSoftware.TypeUtilities 1.2.0

J4JSoftware.TypeUtilities

Provides mechanisms for filtering types during dependency injection registration. While developed to work with Autofac the filtering routines should work with other DI frameworks as well.

The library repository is available on github.

That same link also provides documentation of how these utilities are used by my Autofac-based DI/IHost library.

Overview

I love Autofac, a powerful dependency injection library for C#. I use it in almost all of my projects. It makes egistering concrete types as either specific interface implementations or as themselves a snap.

There are a few ways its use can be simplified, though, in some use cases. That's what this library aims to do: make it relatively straightforward to specify various kinds of type filter conditions, so you can register all the classes that match the conditions at once.

I've designed this library so that it is not dependent on Autofac. While I've only implemented its capabilities for Autofac, you are welcome to adapt them to whatever DI framework you use.

Example

private void SetupDependencyInjection( HostBuilderContext hbc, ContainerBuilder builder )
{
    var typeTests = new TypeTests<IImportData>()
                    .AddTests( PredefinedTypeTests.NonAbstract )
                    .AddTests( PredefinedTypeTests.NonGeneric )
                    .AddTests( new FilterTypeTester<IImportData>( RequireSheetTypeAttribute ) );

    builder.RegisterTypeAssemblies<IImportData>( typeTests );
}

private bool RequireSheetTypeAttribute( Type toCheck ) =>
    toCheck.GetCustomAttribute<SheetTypeAttribute>( false ) != null;

This sequence will register all the concrete types in the assembly which defines the IImportData interface which:

• are not abstract
• are not generic
• are decorated with a non-inherited SheeteTypeAttribute

Architecture

The tests are executed by an instance of TypeTests, which implements the ITypeTester interface. That interface contains a single method call, which returns true if a supplied type meets all the requirements and false if it doesn't:

public interface ITypeTester
{
    bool MeetsRequirements( Type toTest );
}

TypeTesters implements the same interface, iterating over all the individual tests that were added to its instance. Those tests are added by calling one or more extension methods:

Predefined Tests

There are a number of tests I use quite frequently so I created predefined tests that are characterized by the PredefinedTypeTests enum:

Creating Your Own Test

Creating a custom test is easy: just create a class which implements ITypeTester:

public interface ITypeTester
{
    bool MeetsRequirements( Type toTest );
}