How to pass the value of a variable to another class?

Friends, I need to pass the value of a variable to another class.
I am consuming a web API. The user uses a document called CPF to access the application. The CPF is an 11-digit number.

After entering the system, the user is redirected to a class called class_api.dart. I need to get the CPF number and assemble the final part of the url.

This is my login.dart class

import 'dart:js';

import 'package:flutter/material.dart';
import 'package:totem_cfc/aula/class_day.dart';
import 'package:totem_cfc/ui/alerta.dart';
import 'package:totem_cfc/ui/login_api.dart';

class Login extends StatelessWidget {
  final _ctrlCpf = TextEditingController();
  final _formKey = GlobalKey<FormState>();

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Access", style: TextStyle(color: Colors.white)),
        centerTitle: true,
      body: _body(context),

  _body(BuildContext context) {
    return Form(
      key: _formKey,
      child: ListView(children: <Widget>[
        _textFormField("CPF", "CPF",
            controller: _ctrlCpf, validator: _validaCpf),
        _raisenButton("Login",, context),

    String label,
    String hint, {
    TextEditingController controller,
    FormFieldValidator<String> validator,
  }) {
    return TextFormField(
      controller: controller,
      validator: validator,
      decoration: InputDecoration(
        labelText: label,
        hintText: hint,

  String _validaCpf(String texto) {
    if (texto.isEmpty) {
      return "Login";
    if (texto.length < 3) {}

  _raisenButton(String texto, Color cor, BuildContext context) {
    return RaisedButton(
      color: cor,
      child: Text(
        style: TextStyle(
          color: Colors.white,
          fontSize: 20,
      onPressed: () {

  Future<void> _clickButton(BuildContext context) async {
    bool formOk = _formKey.currentState.validate();

    if (!formOk) {

    String cpf = _ctrlCpf.text;
    var usuario = await LoginApi.login(cpf);

    if (usuario != null) {
      _navegaAula(context, cpf);
    } else {
      alert(context, "Login Invalid");

  _navegaAula(BuildContext context, cpf) {

    Navigator.push(context, MaterialPageRoute(builder: (context) => List()));

My class_api.dart looks like this:

import 'dart:convert';
import 'package:totem_cfc/aula/class.dart';
import 'package:http/http.dart' as http;
import 'package:totem_cfc/ui/login.dart';

class ClassApi {
   static Future<List<Class>>  getClass() async {
    List<Class> aulas;
    var prefs = await SharedPreferences.getInstance();
    String token = (prefs.getString("tokenJWT") ?? "");
    print("token jwt: $token");
    var header = {
      "Content-Type": "application/json",
      "Authorization": "Bearer $token"
    var url = Uri.parse("");    
    var response = await http.get(url, headers: header);

    print("status code : ${response.statusCode}");

    if (response.statusCode == 200) {
      List listaResponse = json.decode(response.body);
      classes = List<Class>();

      for (Map map in listaResponse) {
        Classes a = Classes.fromJson(map);
    } else {
      print("erro: ${url}");

    return classes;


So that would be my question. How to receive the cpf by parameter, for example. That way, I could add it to the url.
I appreciate any comments!