当激活结果为空时，不会调用Ninject ActivationStrategy

Question

我可能对ActivationStrategy的行为有一些误解。以下是解释它的代码：

void Main()
{
    var kernel = new StandardKernel();
    kernel.Settings.AllowNullInjection = true;
    kernel.Components.Add<IActivationStrategy, NinjectLoggingStrategy>();
    kernel.Bind<C>().ToProvider(new CallbackProvider<C>(ctx =>
    {
//              return null;
        return new C();
    }));

    kernel.Get<A>();
}

public class A {public A(B b){}}
public class B {public B(C c){}}
public class C {}

public class NinjectLoggingStrategy : ActivationStrategy
{
    private static string RequestPath(IRequest request)
    {
        if (request == null) return "";
        var parentRequest = request.ParentRequest;
        return RequestPath(parentRequest) + " => " + request.Service.Name;
    }

    public override void Activate(IContext context, InstanceReference reference)
    {
        var parentRequest = context.Request.ParentRequest;
        var parentReference = parentRequest == null ? "" : parentRequest.Service.FullName;

        Console.WriteLine("Activating: " + reference.Instance.GetType().FullName);
        Console.WriteLine("Activation Path: " + RequestPath(context.Request));
        base.Activate(context, reference);
    }
}

结果是：

Activating: UserQuery+C
Activation Path:  => A => B => C
Activating: UserQuery+B
Activation Path:  => A => B
Activating: UserQuery+A
Activation Path:  => A

上面是Linqpad中编写的整个代码，请注意CallBackProvider中返回null的行，此行现已注释掉。

  

// return null;

如果我取消评论此行，结果将是：

Activating: UserQuery+B
Activation Path:  => A => B
Activating: UserQuery+A
Activation Path:  => A

我的理解是，无论激活结果如何，都应始终调用ActivationStrategy。