flutterにスプラッシュ画面を追加する話

flutter create flutter_splash_sample

cd flutter_splash_sample
flutter run

flutter pub add flutter_native_splash

flutter_native_splash:
  color: "0021FF"
  # image: "assets/images/splash.png"
  # ↑画像表示させるときは任意のフォルダに画像を格納してパスを記載する

flutter pub run flutter_native_splash:create

～中略～
╔════════════════════════════════════════════════════════════════════════════╗
║                                 WHAT IS NEW:                               ║
╠════════════════════════════════════════════════════════════════════════════╣
║ You can now keep the splash screen up while your app initializes!          ║
║ No need for a secondary splash screen anymore. Just use the remove()       ║
║ method to remove the splash screen after your initialization is complete.  ║
║ Check the docs for more info.                                              ║
╚════════════════════════════════════════════════════════════════════════════╝

Native splash complete. 👍
Now go finish building something awesome! 💪 You rock! 🤘🤩

import 'package:flutter/material.dart';
import 'package:flutter_native_splash/flutter_native_splash.dart'; // ★

void main() {
  // Start★
  WidgetsBinding widgetsBinding = WidgetsFlutterBinding.ensureInitialized();
  FlutterNativeSplash.preserve(widgetsBinding: widgetsBinding);
  // End★
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }
  // Start★
  @override
  void initState() {
    super.initState();
    initialization();
  }

  void initialization() async {
    print('ready in 3...');
    await Future.delayed(const Duration(seconds: 1));
    print('ready in 2...');
    await Future.delayed(const Duration(seconds: 1));
    print('ready in 1...');
    await Future.delayed(const Duration(seconds: 1));
    print('go!');
    FlutterNativeSplash.remove();
  }
  // End★
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}