C＃中的图形图表

Question

我正在尝试使用C＃制作图形图表。但是我有这样的错误信息

Error System.InvalidOperationException: Operation is not valid du to the current state of the object.
at Oracle.DataAccess.Client.OracleCommand.ExecuteReader(Boolean requery, Boolean fillRequest, CommandBehavior behavior)
at Oracle.DataAcess.Client.OracleCommand.ExecuteReader()
at WindowsFormsApplication1.Form3.btnLOAD_Click(Object sender, EventArgs e) in ....

我已经尽力解决了这个问题，但是我没有找到纠正我的编码程序的方法。请问有人在这里可以帮助我纠正此问题吗？ 谢谢。 这是我的代码

try
        {
            con.Open();
            OracleCommand command = new OracleCommand();
            command.Connection = connection;
            string query = "SELECT * FROM TMCI_QC_LINE";
            command.CommandText = query;

            OracleDataReader dr = command.ExecuteReader();
            while (dr.Read())
            {
                chart1.Series["QTY_NG"].Points.AddXY(Convert.ToInt32(dr["ITM_CD"].ToString()), Convert.ToInt32(dr["QTY_NG"].ToString()));
            }
            con.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error " + ex);
        }