Generic type madness

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C#

I am having a really bad time with the following code (simplified version of what is in RaptorDB):

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

namespace genericview
{
    public class Iapi // api class 
    {
        public int I;
    }
    public class vbase // view base type
    {
        public string Name;
    }

    public delegate void MapFunc<V>(Iapi i, V doc);
    public class View<T> : vbase // generic view
    {
        public MapFunc<T> Mapper;
    }

    public class A // base type 
    {
        public int I;
    }

    public class B : A // a subclass
    {
        public int J;
    }

    public class vhandler // view handler
    {
        public vbase view;

        public void insert<T>(T doc) // where the magic should be
        {
            Iapi api = new Iapi();

            View<T> v = (View<T>)view; // exception here the second time round

            v.Mapper(api, doc);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            View<A> va = new View<A>();

            va.Name = "a handler";
            va.Mapper = (api, d) =>
            {
                api.I = d.I;
            };

            vhandler vh = new vhandler();
            vh.view = va;

            A a = new A();
            a.I = 10;
            vh.insert(a); // call the insert -> ok

            B b= new B();
            b.I = 100;
            vh.insert(b); // error when calling here
        }
    }
}

Now the problem is that the second call with a subclass of A is not recognized and an exception is raised of an invalid cast from View to a View<A>.

Any clue how to get this fixed or somehow call the v.Mapper with a derived type of A (namely B)?