Error still occurs even after registering the required dependency, what is wrong?

The following code simulates the problem. I do register the dependency but errors still occur.

using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddSingleton<IFoo, Foo>();

var app = builder.Build();

app.MapGet("/", ([FromServices] Foo f) =>
{
    f.Print();
    return "Hello World!";
});

app.Run();


public interface IFoo
{
    void Print();
}


public class Foo : IFoo
{
    public void Print()
    {
        System.Console.WriteLine("Foo's Print()");
    }
}

InvalidOperationException: No service for type ‘Foo’ has been registered.
Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)

I created the app with dotnet new web -o MyProjectName.

>Solution :

Check the signature of ServiceCollectionServiceExtensions.AddSingleton<TService,TImplementation>(IServiceCollection):

TService – The type of the service to add.
TImplementation – The type of the implementation to use.

You have registered IFoo, not Foo so resolve the interface:

app.MapGet("/", ([FromServices] IFoo f) =>
{
    f.Print();
    return "Hello World!";
});

P.S.

You should be able to skip the FromServicesAttribute because Minimal API handler support implicit resolution from the DI, i.e. (IFoo f) => ... .