private void btnimport_Click(object sender, EventArgs e)
 {
     NhapXuatDuLieu nhapDL = new NhapXuatDuLieu();
     nhapDL.OnImport += new NhapXuatDuLieu.OnImportHandler(updateAll);
     nhapDL.NhapDuLieu();
 }
 private void btnexport_Click(object sender, EventArgs e)
 {
     NhapXuatDuLieu xuatDL = new NhapXuatDuLieu();
     xuatDL.xuatDuLieu();
 }