A generic service provider to simplify Controller constructors and testing in ASP.NET MVC.

IServiceProvider.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public interface IServiceProvider
{
    T GetService<T>() where T : class;
}

SampleController.cs

public class SampleController : Controller
{
    protected readonly IServiceProvider _serviceProvider;
    
    public SampleController(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }
    
    public ActionResult Index()
    {
        // If the service is used across multiple actions,
        // this line can be moved to the constructor and setup with a protected variable 
        var userService = _serviceProvider.GetService<IUserProvider>();
        
        ViewData.Model = userService.GetUser("jbubriski");
        
        return View();
    }
}

ServiceProvider.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;

/// <summary>
/// Default implementation of IServiceProvider.
/// Uses MVC's built in DependencyResolver to get a requested service.
/// In my app I used Ninject, but you should be able to use anything compatible with the DependencyResolver.
/// </summary>
public class ServiceProvider : IServiceProvider
{
    private Dictionary<Type, object> _services = new Dictionary<Type, object>();

    public T GetService<T>() where T : class
    {
        var serviceType = typeof(T);

        if (!_services.ContainsKey(serviceType))
        {
            var service = DependencyResolver.Current.GetService(serviceType);

            _services.Add(serviceType, service);
        }

        return (T)_services[serviceType];
    }
}

TestServiceProvider

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Hosting;
using Moq;

/// <summary>
/// Implementation of IServiceProvider for testing with Moq.
/// Provides easy access to mocks, and the service provider interface returns the mocked services.
/// </summary>
public class TestServiceProvider : ISfcServiceProvider
{
    private Dictionary<Type, object> _mocks = new Dictionary<Type, object>();

    public T GetService<T>() where T : class
    {
        var serviceType = typeof(Mock<T>);

        if (!_mocks.ContainsKey(serviceType))
        {
            var service = new Mock<T>();

            _mocks.Add(serviceType, service);
        }

        return (T)((Mock<T>)_mocks[serviceType]).Object;
    }

    public Mock<T> GetMock<T>() where T : class
    {
        var serviceType = typeof(Mock<T>);

        if (!_mocks.ContainsKey(serviceType))
        {
            _mocks.Add(serviceType, new Mock<T>());
        }

        return (Mock<T>)_mocks[serviceType];
    }
}