Creating a document in Firestore from Flutter

create.dart

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';

class TODOCreate extends StatefulWidget {

  @override
  State<StatefulWidget> createState() {
    return TODOCreateState();
  }
}

class TODOCreateState extends State<TODOCreate> {

  final collection = Firestore.instance.collection('tasks');
  final TextEditingController controller = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Create a task')),
      body: Center(
          child: Padding(
              padding: EdgeInsets.all(16),
              child: TextField(
                  autofocus: true,
                  controller: controller,
                  decoration: InputDecoration(
                      labelText: 'Enter name for your task'
                  )
              )
          )
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.done),
        onPressed: () async {
          // Creating a new document
          await collection.add({'name': controller.text, 'completed': false});
          Navigator.pop(context);
        },
      ),
    );
  }
}

main.dart

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:todo_app/auth.dart';
import 'package:todo_app/login.dart';
import 'package:todo_app/create.dart';
import 'package:todo_app/list.dart';

void main() => runApp(TODOApp());

class TODOApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return TODO();
  }
}

class TODO extends StatefulWidget {

  @override
  State<StatefulWidget> createState() {
    return TODOState();
  }
}

class TODOState extends State<TODO> {

  final Authentication auth = new Authentication();
  FirebaseUser user;

  void onLogin(FirebaseUser user) {
    setState(() {
      this.user = user;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'TODO app',
      initialRoute: '/',
      routes: {
        '/': (context) => TODOLogin(onLogin: onLogin),
        '/list': (context) => TODOList(),
        '/create': (context) => TODOCreate(),
      },
    );
  }
}