如何解决这个问题？ （已经有一个与此Connection关联的开放DataReader，必须先关闭）

Question

Public Sub chartall(ByVal chart1 As Object)
    conn()
    Dim str As String = "SELECT department as 'DEPARTMENT', COUNT(CASE WHEN voterstatus = '1' THEN 1 END) AS 'VOTED', COUNT(CASE WHEN voterstatus = '0' THEN 1 END) AS 'NOT YET VOTED' FROM tblvoter GROUP BY department"
    Dim cmd As New MySqlCommand(str, myconnection)
    Dim dr As MySqlDataReader = cmd.ExecuteReader()
    Try
        While dr.Read
            chart1.Series("Series1").Points.AddXY(dr.GetString("Course"), dr.GetInt32("COUNT(CASE WHEN voterstatus = '1' THEN 1 END)"))
        End While
    Catch ex As Exception
        cmd.ExecuteNonQuery()
        cmd.Dispose()
    End Try
End Sub

我不知道我的代码有什么问题。我只想把数据放在图表上。