private void refresh_form()
{
m_sle_chon_nhan_vien.EditValue = null;
m_sle_cach_tinh_thue.EditValue = null;
m_sle_loai_thu_nhap.EditValue = null;
m_txt_ly_do.Text = "";
m_txt_so_tien.Text = "";
m_txt_chon_thang.Text = DateTime.Now.Month.ToString();
m_txt_chon_nam.Text = DateTime.Now.Year.ToString();
}