private void txtIDNV_TextChanged(object sender, TextChangedEventArgs e)
 {
     if (txtIDNV.Text != "")
     {
         NhanVien nv  = new NhanVien();
         var      nv1 = nv.LayNV(txtIDNV.Text);
         if (nv1 != null)
         {
             txtIDNV.Text     = nv1.manv;
             txtTenNV.Text    = nv1.tennv;
             txtCMNDNV.Text   = nv1.cmnd;
             txtDiaChi.Text   = nv1.diachi;
             txtGioiTinh.Text = nv1.gioitinh;
             txtNgSinh.Text   = nv1.ngaysinh.Value.Date.ToString("dd/MM/yyyy");
             txtSDT.Text      = nv1.sdt;
         }
     }
 }