When the WinForm is loaded, there is nine pieces of records in the ultragrid. then I click the ultraButton1 to delete the second data row, and it displays eight  pieces of records
in the ultragrid right now, but I click ultraButton2, the MessagBox show  nine pieces of records, and run the code this.Text=m_dt.Rows[1]["UnitCode"], throw an error(System.Data.DeletedRowInaccessibleException).
Now how to let the deleted row is removed from this.ultraGrid1.DataSource  when I execute m_dt = (DataTable)this.ultraGrid1.DataSource?

All the codes as below:

        private void Form1_Load(object sender, EventArgs e)
        {
            SqlExecuteMaster SqlOP = new SqlExecuteMaster();
            DataTable dt = new DataTable();
            string strSql = "Select UnitCode,UnitName,remark from Pb_unit";
            dt = SqlOP.GetDataTable(strSql);// generate datatable
            this.ultraGrid1.DataSource = dt;
        }

        private void ultraButton1_Click(object sender, EventArgs e)
        {
            this.ultraGrid1.Rows[1].Delete(false);
            this.ultraGrid1.Refresh();
        }

        private void ultraButton2_Click(object sender, EventArgs e)
        {
            DataTable m_dt = new DataTable();
            m_dt = (DataTable)this.ultraGrid1.DataSource;
            MessageBox.Show(m_dt.Rows.Count.ToString());
            this.Text=m_dt.Rows[1]["UnitCode"];
        }