private void txttracuu_TextChanged(object sender, EventArgs e)
 {
     if (txttracuu.Text.Trim() == "")
     {
         List <TaiKhoan_DTO> lstTK = TaiKhoan_BUS.LayDSTK();
         DgvTaiKhoan.DataSource = lstTK;
     }
     else
     {
         dieukien = "TaiKhoan";
         List <TaiKhoan_DTO> lstTimKiem = TaiKhoan_BUS.Timtaikhoan(dieukien, txttracuu.Text);
         DgvTaiKhoan.DataSource = lstTimKiem;
     }
 }