[Flutter] Firebase と連携し Firestore へデータ追加 ( Manual Install ver ）

# platform :ios, '9.0'
platform :ios, '10.12'

import 'package:flutter/material.dart';

import 'package:firebase_core/firebase_core.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firestore Add Sample',
      home: FirestoreSave(),
    );
  }
}

class FirestoreSave extends StatefulWidget {
  @override
  _MyFirestorePageState createState() => _MyFirestorePageState();
}

class _MyFirestorePageState extends State<FirestoreSave> {
  @override
  Widget build(BuildContext context) {

    CollectionReference users = FirebaseFirestore.instance.collection('users');

    Future<void> addFirestoreUser() {
      // Call the user's CollectionReference to add a new user
      return users
          .add({
            'full_name': "fullName",
            'company': "company",
            'age': "age" 
          })
          .then((value) => print("User Added"))
          .catchError((error) => print("Failed to add user: $error"));
    }

    return Scaffold(
      appBar: AppBar(
        title: Text("title"),
      ),
       body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              'Body'
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: addFirestoreUser,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

Exception has occurred.
FirebaseException ([core/not-initialized] Firebase has not been correctly initialized.

Usually this means you've attempted to use a Firebase service before calling `Firebase.initializeApp`.

View the documentation for more information: https://firebase.flutter.dev/docs/overview#initialization
    )

rules_version = '2';
service cloud.firestore {
    match /databases/{database}/documents {
        match /{document=**} {
          allow read, write: if false;
        }
    }
}

rules_version = '2';
service cloud.firestore {
    match /databases/{database}/documents {
        match /{document=**} {
          allow read, write: if
              request.time < timestamp.date(2022, 3, 28);
        }
    }
}

rules_version = '2';

service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if request.auth != null;
    }
  }
}