private void simpleButtonthem_Click(object sender, EventArgs e)
 {
     if (ClassTaiKhoan.KTThemTK(txttaikhoan.Text, txtmatkhau.Text, comboboxmanv.Text) == true)
     {
         tk.ThemTK(txttaikhoan.Text, txtmatkhau.Text, comboboxmanv.Text);
         FormTaiKhoan_LoadData();
     }
 }
 private void simpleButtonxoa_Click(object sender, EventArgs e)
 {
     if (ClassTaiKhoan.KTXoaTK(comboboxmanv.Text) == true)
     {
         tk.XoaTK(comboboxmanv.Text);
         FormTaiKhoan_LoadData();
     }
 }
 public FormTaiKhoan()
 {
     tk = new ClassTaiKhoan();
     FormTaiKhoan_LoadData();
     InitializeComponent();
 }