问什么是Ninject，你什么时候使用它？

EN

public interface IService
{
    void Serve();
}
public class Service1 : IService
{
    public void Serve() {
        Console.WriteLine("Service1 Called");
    }
}
public class Service2 : IService
{
    public void Serve() {
        Console.WriteLine("Service2 Called");
    }
}
public class Service3 : IService
{
    public void Serve() {
        Console.WriteLine("Service3 Called");
    }
}
public class Client
{
    private IService service;

    public Client(IService _service)   //Constructor injection
    {
        service = _service;
    }
    public void ServeMethod() {
        service.Serve();  //Notice here, this Serve() method has no idea what to do.
    }                     // runtime will assign the object, that is Ninject
}


class Program
{
    static void Main(string[] args)
    {
        IService s1 = new Service1();  //N.B. Ninject assigns object with interface 

        Client c1 = new Client(s1);    

        c1.ServeMethod();         

        IService s2 = new Service2();  //N.B. Ninject assigns object with interface

        c1 = new Client(s2);

        c1.ServeMethod();

        IService s3 = new Service3(); //N.B. Ninject assigns object with interface

        c1 = new Client(s3);

        c1.ServeMethod();


        Console.ReadKey();
    }
}       
  // Ninject creates object in runtime for interface in runtime in ASP.NET MVC project.