这个递归调用，n只等于1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;
namespace BinaryTree
{
    public class Tree<TItem> where TItem : IComparable<TItem>
    {
        public Tree(TItem nodeValue)
        {
            this.NodeData = nodeValue;
            this.LeftTree = null;
            this.RightTree = null;
        }

        public void Insert(TItem newItem)
        {
            TItem currentNodeValue = this.NodeData;
            if ((newItem) > 0)
            {
                if (this.LeftTree == null)
                {
                    this.LeftTree = new Tree<TItem>(newItem);
                }
                else
                {
                    this.LeftTree.Insert(newItem);
                }
            }
            else
            {
                if (this.RightTree == null)
                {
                    this.RightTree = new Tree<TItem>(newItem);
                }
                else
                {
                    this.RightTree.Insert(newItem);
                }
            }
        }

        public void WalkTree()
        {
            if (this.LeftTree != null)
            {
                this.LeftTree.WalkTree();
               
            }

            Console.WriteLine(this.NodeData.ToString());
            n++;//n每递归一次后，又返回到0
            
            if (this.RightTree != null)
            {
                this.RightTree.WalkTree();
            }
        }

        public TItem NodeData { get; set; }
        public Tree<TItem> LeftTree { get; set; }
        public Tree<TItem> RightTree { get; set; }

      
        public int n=0;
    }
}

明白了，因为每递归一次，类就实例化一次，而n是在类中定义的。

定义成静态不就好了