How to Subscribe to a Constructor in vNext Dependency Injection

I am experimenting with a one-off vNext app. What I am trying to do is create a dummy class called "DataService" that will return some data and then create objects that use DI to accept the IDataService parameter as a constructor.

So, my IDataService / DataService definitions are:

public interface IDataService
{
    DateTime Created { get; }

}

public class DataService : IDataService
{
    private DateTime created = DateTime.Now;
    public DateTime Created
    {
        get { return created; }
    }

}

      

        
        
        
      

    

In my startup class, I register this as a singleton:

public void Configure(IApplicationBuilder app)
    {
        app.UseServices(services =>
        {
            services.AddSingleton<Data.IDataService, Data.DataService>();
        });

      

        
        
        
      

    

And in the class I created, I add the IDataService interface as a constructor dependency:

internal class Constraint : IRouteConstraint
{
    private readonly IDataService _dataService;
    public Constraint (IDataService dataService)
    {
        _dataService = dataService;
    }
    public bool Match(....)
    {
       //call dataservice for match
    }
}

      

        
        
        
      

    

The class here with constructor dependencies is IRouteConstraint which I am trying to use to get dynamic routes in MVC - the last part of the launcher class code looks like this:

 app.UseMvc(routes => {
            routes.MapRoute(name: "TestRoute", template: "{*constraints}", defaults: new { controller = "Test", action = "Index" }, constraints: new { constraint = new Constraint() }); //<--- how to construct using DI?

        });

      

        
        
        
      

    

The problem is that the Constraint () class cannot be instantiated because the constructor is missing. All examples show a controller using DI, and the instantiation of Controller classes is handled by MVC, so this is a part of "automagic" that we don't see at first glance.

So my question is:

• How do I instantiate a 'Constraint' object so that the DI provides an implementation of the DataService syntax?
• Is my problem because I am trying to use this in the Configure method in the UseMvc method, or is my problem more fundamental?

I suppose I am missing some way to make DI act like a factory object to provide my objects rather than declaratively creating them.