点btn1，就执行updatedatebase方法，可是没任何反映
分析得出this.myds.HasChanges（）结果是 false，this.myds.GetChanges()这个对象得到的也是null
为什么会这样？逻辑那里出了问题，请大虾指教指教

using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace database
{
    public partial class Form1 : Form
    {


        public SqlDataAdapter myda = new SqlDataAdapter();
        public DataSet myds = new DataSet();
        public SqlCommandBuilder sqlcmdbld;
     
        public Form1()
        {
            InitializeComponent();

            SqlConnection sqlconn = new SqlConnection("server=LENOVO-1389D547;database=master;uid=sa;pwd=8233");
            SqlDataAdapter myda = new SqlDataAdapter("select * from student", sqlconn);

            DataSet myds = new DataSet();

            myda.Fill(myds, "stu");
           
            dataGridView1.DataSource = myds.Tables["stu"];
           

        }
        
        
      
        
        
        public DataSet updatedatebase(DataSet changedata)
    {

      
        this.sqlcmdbld = new SqlCommandBuilder(myda);
        myda.Update(changedata);
        return changedata;

        
        
        }
 private void btn1_Click(object sender, EventArgs e)
        {if (this.myds.HasChanges())
        {
this.updatedatebase(this.myds.GetChanges());
MessageBox.Show("修改成功");

        

        }
        
        
        }
    }
}

杂没人回答呢

是的，dataGridView1已经显示数据了，就是点BTN1按钮的时候
提示this.myds.GetChanges()是个空值？？

是的，怎么让datagridview1与myds绑定在一起？？？