C#连接Sybase数据库

try
{
    DataTable dt = new DataTable();
    AseConnection con = new AseConnection(SYBaseConnectionStr);
    AseCommand cmd = con.CreateCommand();
    cmd.CommandText = "select * from clinic_invoice_detail where expense_date between @date1 and @date2";
    cmd.Parameters.Add(new AseParameter("@date1", AseDbType.DateTime) { Value = txt_dateStart.Value });
    cmd.Parameters.Add(new AseParameter("@date2", AseDbType.DateTime) { Value = txt_dateEnd.Value });
    AseDataAdapter da = new AseDataAdapter(cmd);
    da.Fill(dt);
    da.Dispose();
    cmd.Dispose();
    con.Dispose();
    dataGridView1.DataSource = dt;
    dataGridView1.AutoResizeColumns();
}
catch (Exception ex)
{
    MessageBox.Show(ex.ToString());
}