Command对象修改数据有问题
protected void Page_Load(object sender, EventArgs e)
  {
  if (!IsPostBack)
  {
  this.bind();
  }  
  }
  public SqlConnection GetConnection()
  {
  string myStr = ConfigurationManager.AppSettings["ConnectionString"].ToString();
  SqlConnection myConn = new SqlConnection(myStr);
  return myConn;
  }
  protected void bind()
  {
  SqlConnection myConn = GetConnection();
  myConn.Open();
  string sqlStr = "select * from tb_Class ";
  SqlDataAdapter myDa = new SqlDataAdapter(sqlStr, myConn);
  DataSet myDs = new DataSet();
  myDa.Fill(myDs);
  GridView1.DataSource = myDs;
  GridView1.DataKeyNames = new string[] { "ClassID" };
  GridView1.DataBind();
  myDa.Dispose();
  myDs.Dispose();
  myConn.Close();
  }
  protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
  {
  GridView1.EditIndex = e.NewEditIndex;这句什么意思?
  this.bind();
  }
  protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
  {
  int ClassID = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Value.ToString());这句是不是设置成当前选中的索引值?
  string CName = ((TextBox)(GridView1.Rows[e.RowIndex].Cells[2].Controls[0])).Text.ToString();这句什么意思?  
  string sqlStr = "update tb_Class set ClassName='" + CName + "' where ClassID=" + ClassID;
  SqlConnection myConn = GetConnection();
  myConn.Open();
  SqlCommand myCmd = new SqlCommand(sqlStr, myConn);
  myCmd.ExecuteNonQuery();
  myCmd.Dispose();
  myConn.Close();
  GridView1.EditIndex = -1;为什么这里有减1?
  this.bind();
  }
  protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
  {
  GridView1.EditIndex = -1;为什么这里有减1?
  this.bind();
  }

------解决方案--------------------
GridView1.EditIndex = e.NewEditIndex;这句是获取当前选中的要编辑行的索引。
int ClassID = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Value.ToString());这句是根据索引值获取classID，
 string CName = ((TextBox)(GridView1.Rows[e.RowIndex].Cells[2].Controls[0])).Text.ToString();这句是获取CName，
GridView1.EditIndex = -1;这句是把GridView1的索引值置空，
------解决方案--------------------
GridView1.EditIndex = e.NewEditIndex;是获取当前选中行的索引，进行编辑状态操作。
int ClassID = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Value.ToString());这是根据索引获取此行主键ClassID 的值
string CName = ((TextBox)(GridView1.Rows[e.RowIndex].Cells[2].Controls[0])).Text.ToString();这是根据索引获取此行CName 的值
GridView1.EditIndex = -1;取消编辑状态 获取或设置要编辑的行的索引。默认值为 -1，指示没有正在编辑的行从0开始索引。
------解决方案--------------------
上面都已經說很清楚了。