private void chkChiPhi_CheckedChanged(object sender, EventArgs e)
 {
     if (chkTQ_ChiPhi.Checked)
     {
         LineSeries lineNhapHang = new LineSeries();
         lineNhapHang.Name   = "lineChiPhi";
         lineNhapHang.Title  = "Chi phí";
         lineNhapHang.Values = new ChartValues <double> {
         };
         for (int i = 1; i <= 12; i++)
         {
             lineNhapHang.Values.Add(PhieuNhapBUS.LayDoanhSoPhieuNhapTheoThang(i));
         }
         chartTongQuat.Series.Add(lineNhapHang);
     }
     else
     {
         LineSeries line = null;
         foreach (LineSeries ls in chartTongQuat.Series)
         {
             if (ls.Name == "lineChiPhi")
             {
                 line = ls;
             }
         }
         chartTongQuat.Series.Remove(line);
     }
 }
 private void chkTQ_LoiNhuan_CheckedChanged(object sender, EventArgs e)
 {
     if (chkTQ_LoiNhuan.Checked)
     {
         LineSeries lineLoiNhuan = new LineSeries();
         lineLoiNhuan.Name   = "lineLoiNhuan";
         lineLoiNhuan.Title  = "Lợi nhuận";
         lineLoiNhuan.Values = new ChartValues <double> {
         };
         for (int i = 1; i <= 12; i++)
         {
             lineLoiNhuan.Values.Add(HoaDonBUS.LayDoanhSoHoaDonTheoThang(i) - PhieuNhapBUS.LayDoanhSoPhieuNhapTheoThang(i));
         }
         chartTongQuat.Series.Add(lineLoiNhuan);
     }
     else
     {
         LineSeries line = null;
         foreach (LineSeries ls in chartTongQuat.Series)
         {
             if (ls.Name == "lineLoiNhuan")
             {
                 line = ls;
             }
         }
         chartTongQuat.Series.Remove(line);
     }
 }