How to use Func in built-in dependency injection

Question

Using asp.net 5 I\'d like my controller to be injected with a Funcinstead of T

For example:

Answer 1

There are a few options available to you, the first is you can switch over to use the incredible Lamar (with it's ASP.NET Core integration).

For the most part, switching to Lamar is a few lines of code, and you'll be able to resolve Func<> and Lazy<> all day long.

I've been using it at scale for a while on a large microservices based platform and we're completely happy with it *.

If you don't want to move over to Lamar, you can use this for resolving Lazy<> (sorry, I've tried and tried, and I can't get it to work with Func<>:

// Add to your Service Collection.
services.AddTransient(typeof(Lazy<>), typeof(LazyServiceFactory<>));

class LazyServiceFactory : Lazy
{
    public LazyServiceFactory(IServiceProvider serviceProvider)
        : base(() => serviceProvider.GetRequiredService())
    {
    }
}

And just for completeness, here's a test too.

// And some tests...
[TestMethod]
[DataTestMethod]
[DataRow(ServiceLifetime.Transient)]
[DataRow(ServiceLifetime.Scoped)]
[DataRow(ServiceLifetime.Singleton)]
public void Resolve_GivenLazyilyRegisteredService_CanResolve(ServiceLifetime serviceLifetime)
{
    // Arrange
    IServiceProvider serviceProvider = CreateServiceProvider(serviceLifetime);
    using IServiceScope scope = serviceProvider.CreateScope();

    // Act
    Func> result = () => scope.ServiceProvider.GetRequiredService>();

    // Assert
    result
        .Should()
        .NotThrow()
        .And
        .Subject()
        .Value
        .Should()
        .NotBeNull();
}

static IServiceProvider CreateServiceProvider(ServiceLifetime serviceLifetime)
{
    IServiceCollection services = new ServiceCollection();

    services.Add(new ServiceDescriptor(typeof(Lazy<>), typeof(LazyServiceFactory<>), serviceLifetime));

    services.Add(new ServiceDescriptor(typeof(ClassHello), typeof(ClassHello), serviceLifetime));

    return services.BuildServiceProvider(true);
}

I've not put this through it's paces as I use Lamar pretty much exclusivly now, but this has come in handy for smaller/ disposable projects.

* My only minor issue is that it doesn't support IAsyncDisposable yet.