错误 1 当前上下文中不存在名称“btn_Click” d:\用户目录\我的文档\visual studio 2010\Projects\ch06\ch06\M

using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using ch06.Examples;

namespace ch06
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
            this.StartPosition = FormStartPosition.CenterScreen;
            foreach(var v in this.Controls)
            {
                Button btn=v as Button;
                if(btn!=null)
                {
                   btn.Click +=btn_Click;
                }
            }
        }

         void button1_Click(object sender, EventArgs e)
         {
             string s=(sender as Button).Text;
             switch(s)
             {
                 case"例1":
                     EnvironmentExample fm1=new EnvironmentExample();
                     fm1.ShowDialog();
                     break;
             }
         }
    }
}