GridView控件RowUpdating问题。

为什么控件编辑状态下点击更新就会出现索引超出范围的错误？

后台代码如下：

    protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        string strID = GridView1.DataKeys[e.RowIndex].Value.ToString();
        string strNAME = ((TextBox)GridView1.Rows[e.RowIndex].Cells[1].Controls[0]).Text;
        string strCS = ((TextBox)GridView1.Rows[e.RowIndex].Cells[2].Controls[0]).Text;
        string strMATH = ((TextBox)GridView1.Rows[e.RowIndex].Cells[3].Controls[0]).Text;
        string strENG = ((TextBox)GridView1.Rows[e.RowIndex].Cells[4].Controls[0]).Text;

        string strSQL = "UPDATE SCORES SET NAME='" + strNAME + "',SCORE_CS='" + strCS + "',SCORE_MATH='" + strMATH + "',SCORES_ENG='" + strENG + "' WHERE ID=" + strID;

        conn = new SqlConnection(WebConfigurationManager.AppSettings["conStr"]);
        conn.Open();
        cmd = new SqlCommand(strSQL, conn);
        cmd.ExecuteNonQuery();
        cmd.Dispose();
        conn.Close();
        GridView1.EditIndex = -1;
        GridViewBind();
    }

            protected void GridViewBind()
    {
        string str_con = WebConfigurationManager.AppSettings["conStr"];
        conn = new SqlConnection(str_con);
        conn.Open();
        sda = new SqlDataAdapter("SELECT * FROM SCORES", conn);
        sda.Fill(ds, "ds_SCORES");
        conn.Close();
        GridView1.DataSource = ds.Tables["ds_SCORES"];
        GridView1.DataBind();        
    }

补充：GridView的主键DataKeyNames=也是设置了的。

另外，试了下在RowUpdating方法中输出GridView1.DataKeys.Count和GridView1.Rows.Count，发现都是0。