编程时遇到对象关联API的设计问题，感觉可能这种api的设计方案本身就有问题，所以目前还未有解决方案。

问题如下：

using System;

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

namespace ConsoleApplication

{     /// <summary>     /// 在NotImplement的方法/属性中填入相应内容，以保证程序不会抛出异常。     /// (就是：Parent属性，AddChild方法，RemoveChild方法。)     ///      /// 不能修改其它代码。     /// </summary>     class Program     {         static void Main(string[] args)         {             Parent parentA = new Parent();             Parent parentB = new Parent();             Child child = new Child();

            parentA.AddChild(child);

            child.Parent = parentB;

            Assert(parentA.Children.Count == 0, parentB.Children.Count == 1, child.Parent == parentB);

            parentA.AddChild(child);

            Assert(parentB.Children.Count == 0, parentA.Children.Count == 1, child.Parent == parentA);

            child.Parent = null;

            Assert(parentB.Children.Count == 0, parentA.Children.Count == 0, child.Parent == null);         }

        static void Assert(params bool[] values)

        {             foreach (var value in values)             {                 if (value == false)                 {                     throw new Exception();                 }             }         }     }     class Parent     {         private List<Child> _children;

        public Parent()

        {             this._children = new List<Child>();         }

        public IList<Child> Children

        {             get             {                 return new System.Collections.ObjectModel.ReadOnlyCollection<Child>(this._children);             }         }         public void AddChild(Child child)         {             throw new NotImplementedException();         }         public void RemoveChild(Child child)         {             throw new NotImplementedException();         }

    }

    class Child     {         private Parent _parent;

        public Parent Parent

        {             get             {                 throw new NotImplementedException();             }             set             {                 throw new NotImplementedException();             }         }     } }