内部类，有意思

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

namespace Demo
{   

    public class ClassA
    {
        private int state = -1;
        public int State
        {
            get
            {
                return state;
            }
        }

        public class ClassB // 内部类
        {
            public void SetPrivateState(ClassA target,int newState)
            {
                target.state = newState;
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ClassA myObject = new ClassA();
            Console.WriteLine("myObject.State= {0}",myObject.State);
            ClassA.ClassB myOtherObject = new ClassA.ClassB();
            myOtherObject.SetPrivateState(myObject,100);
            Console.WriteLine("myObject.State= {0}", myObject.State);
            Console.ReadKey();
        }
    }
}

这个很少用，就当图个乐吧!