Dependency injection (DI) in ASP.Net MVC 6

Question

i was reading a write up on easily dependency injection in ASP.Net MVC 6 from this url http://weblogs.asp.net/scottgu/introducing-asp-net-5

they show how very easily we can inject dependency into project

1st one

namespace WebApplication1
{
    public class TimeService
    {
        public TimeService()
        {
            Ticks = DateTime.Now.Ticks.ToString();
        }
        public String Ticks { get; set; }
    }
}


register the time service as a transient service in the ConfigureServices method of the Startup class:

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();
        services.AddTransient<TimeService>();
    }


public class HomeController : Controller
{

    public TimeService TimeService { get; set; }

    public HomeController(TimeService timeService)
    {
        TimeService = timeService;
    }


    public IActionResult About()
    {
        ViewBag.Message = TimeService.Ticks + " From Controller";
        System.Threading.Thread.Sleep(1);
        return View();
    }
}

2nd one

public class HomeController : Controller
{
    [Activate]
    public TimeService TimeService { get; set; }
}

now see the second code. are they trying to say that if we use [Activate] attribute then we do not have to instantiate TimeService by controller constructor injection?

just tell me if we use [Activate] attribute then what will be the advantage ?

if we use [Activate] attribute then what line of code we can eliminate from 1st same code. thanks

Answer 1

The differences between the two code blocks are indeed that the first one leverages Constructor Injection to resolve the dependency on TimeService, while the second example marks a property as one that needs resolving using Property Injection.

What this means is simply that the following constructor becomes redundant:

public HomeController(TimeService timeService)
{
    TimeService = timeService;
}

As to why one would opt for Constructor versus Property Injection, I find that trying to have a list of your dependencies clearly listed out in your constructor highlights when a class becomes too dependent, which raises concerns as to what a class is trying to accomplish and, subsequently, makes it a candidate for refactoring.

Property Injection via [Activate] will not be supported from beta5 onwards.