那位高手帮我看看怎么实现

Question

这是一个数据结构中单链表的实现，代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace ConsoleApplication1
{
    public interface IListDS<T>
    {
        int GetLength();
        void Clear();
        bool IsEmpty();
        void Append( T item );
        void Insert( T item, int i );
        T Delete( int i );
        T GetElem( int i );
        int Locate( T value );
    }    public class Node<T>
    {
        private T data;
        private Node<T> next;        public Node(T val,Node<T> p)
        {
            this.data = val;
            this.next = p;
        }        public Node( Node<T> p )
        {
            this.next = p;
        }        public Node( T val )
        {
            this.data = val;
            this.next = null;
        }        public Node()
        {
            this.data = default(T);
            this.next = null;
        }        public T Data
        {
            get
            {
                return data;
            }
            set
            {
                data = value;
            }
        }        public Node<T> Next
        {
            get
            {
                return this.next;
            }
            set
            {
                this.next = value;
            }
        }
    }    public class LinkList<T>:IListDS<T>
    {
        private Node<T> head;        public Node<T> Head
        {
            get
            {
                return this.head;
            }
            set
            {
                this.head = value;
            }
        }        public LinkList()
        {
            head = null;
        }        public int GetLength()
        {
            int len = 0;
            Node<T> p = head;
            while(p.Next != null)
            {
                p = p.Next;
                ++len;
            }
            return len;
        }        public void Clear()
        {
            head = null;
        }        public bool IsEmpty()
        {
           if(head == null)
            {
                return true;
            }
            else
            {
                return false;
            }
        }        public void Append( T item )
        {
            Node<T> q = new Node<T>(item);
            Node<T> p = new Node<T>();
            if(head == null)
            {
                head = q;
                return;
            }
            p = head;
            while(p.Next != null)
            {
                p = p.Next;
            }
            p.Next = q;        }        public void Insert( T item, int i )
        {
            if(IsEmpty() || i < 1)
            {
                Console.WriteLine("The list is empty or position is error");
                return;
            }
            if(i == 1)
            {
                Node<T> q = new Node<T>(item);
                q.Next = head;
                head = q;
                return;
            }
            int j = 1;
            Node<T> p = head;
            Node<T> r = new Node<T>();
            while(p.Next != null && j < i)
            {
                r = p;
                p = p.Next;
                ++j;
            }
            if(j == i)
            {
                Node<T> q = new Node<T>(item);
                q.Next = p;
                r.Next = q;
            }
        }        public void InsertPost( T item, int i )
        {
            if(IsEmpty() || i < 1)
            {
                Console.WriteLine("The list is empty or position is error");
                return;
            }
            if(i == 1)
            {
                Node<T> q = new Node<T>(item);
                q.Next = head.Next;
                head.Next = q;
                return;
            }
            Node<T> p = head;
            int j = 1;
            while(p.Next != null && j < i)
            {
                p = p.Next;
                ++j;
            }
            if(j == i)
            {
                Node<T> q = new Node<T>(item);
                q.Next = p.Next;
                p.Next = q;
            }
        }        public T Delete( int i )
        {
            if(IsEmpty() || i < 1)
            {
                Console.WriteLine("The list is empty or position is error");
                return default(T);
            }
            Node<T> q = new Node<T>();
            if(i == 1)
            {   
                q = head;
                head.Next = head;
                return q.Data;
            }
            Node<T> p = head;
            int j = 1;
            while(p.Next != null && j < i)
            {
                q = p;
                p = p.Next;
                ++j;
            }
            if(j == i)
            {
                q.Next = p.Next;
                return p.Data;
            }
            else
            {
                Console.WriteLine("The ith node is not exist");
                return default(T);
            }        }        public T GetElem(int i)
        {
            if(IsEmpty() || i < 1)
            {
                Console.WriteLine("List is empty or position is error");
                return default(T);
            }
            Node<T> p = new Node<T>();
            p = head;
            int j = 1;
            while(p.Next != null && j < i)
            {
                p = p.Next;
                ++j;
            }
            if(j == i)
            {
                return p.Data;
            }
            else
            {
                Console.WriteLine("The ith is not exist");
                return default(T);
            }
        }        public int Locate( T value )
        {
            if(IsEmpty())
            {
                Console.WriteLine("List is empty");
                return -1;
            }
            Node<T> p = new Node<T>();
            p = head;
            int i = 1;
            while(p.Next != null && !p.Data.Equals(value))
            {
                p = p.Next;
                ++i;
            }
            return i;        }        public void Reverse()
        {
            Node<T> p = head.Next;
            Node<T> q = new Node<T>();
            head.Next = null;
            while(p != null)
            {
                q = p;
                p = p.Next;
                q.Next = head.Next;
                head.Next = q;
            }
        }
    }    public class Program
    {
        static void Main()
        {
            LinkList<int> L = new LinkList<int>();
            Console.WriteLine(L.IsEmpty());
            Console.WriteLine(L.GetLength());
            L.Append(1);
            L.Insert(2 , 1);
            Console.WriteLine(L.IsEmpty());
            Console.WriteLine(L.GetLength());
            Console.Read();
        }
    }
}我在编译运行后，提示编译错误，public int GetLength(){}未将对象引用设置到对象的实例。该怎么解决？

Answer 1

public int GetLength()
  {
  int len = 0;
  Node<T> p = head;
  while(p != null)
  {
  p = p.Next;
  ++len;
  }
  return len;
  }不会用 Debugger 啊？

Answer 2

除了一楼的办法，还可以把 LinkList构造函数改改，否则new linklist时，head为空，head.next就越界        public LinkList()
        {
            head = new Node<T>();
        }

Answer 3

我在使用了你的方法后，又出现了新的问题，在执行下面的代码时，明显不是正确的结果
  LinkList<int> L = new LinkList<int>();
  Console.WriteLine(L.IsEmpty());
在此时，应输出为 True, 但是输出的是false；。

Answer 4

.net 中已经有了链表的的类了 LinkedList<T> 
不用再自已实现了吧