【Firebase / Flutter Web】firestoreEmulatorとローカル実行アプリを接続する。

環境：Mac Catalina 10.15.7
開発対象：Flutter Web
エディター:Visual Studio Code

main.dartで起動コマンドのオプションにより、分岐させる処理を追加する。

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


void main() async {

  const isEmulator = bool.fromEnvironment('IS_EMULATOR');//追記
  print('start(isEmulator: $isEmulator)');

  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

//以下追記　↓  
  if (isEmulator) {
    /* 起動時にオプションをつけた場合→"--dart-define=IS_EMULATOR=true" */
    FirebaseFirestore.instance.settings = Settings(
      host: 'localhost:58080',//エミュレーターのローカルURL
      sslEnabled: false,
      persistenceEnabled: false,
    );
  }
//ここまで追記　↑ 

  runApp(MyAppHome());
}

launch.jsonにオプション付きで登録しておく

launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "port1234",
            "request": "launch",
            "type": "dart",
            "a,rgs": ["-d", "chrome","--web-port", "1234"],
        },
     //以下追記
        {
            "name": "emu1234",
            "request": "launch",
            "type": "dart",
            "args": ["-d", "chrome","--web-port", "1234","--dart-define=IS_EMULATOR=true"],
        }
    ]
}

参考
https://qiita.com/someone7140/items/26fa2f5710b5b36e537f
https://medium.com/flutter-jp/firebase-emulator-938e9a0cdfad
https://www.filledstacks.com/post/how-to-setup-firebase-emulator-with-flutter/