awaitable_icon_button.dart

import 'package:flutter/material.dart';

class AwaitableIconButton extends StatefulWidget {
  const AwaitableIconButton({
    Key? key,
    required this.onPressed,
    required this.icon,
    this.indicatorWidget,
    this.buttonStyle,
  }) : super(key: key);

  /// 押した時の動作
  /// `null` の場合はボタンが非活性になる
  final Future<void> Function()? onPressed;

  /// ボタンに表示するラベル文字列
  final Widget icon;

  final Widget? indicatorWidget;

  /// ボタンのスタイル設定。任意設定
  final ButtonStyle? buttonStyle;

  @override
  _AwaitableIconButtonState createState() => _AwaitableIconButtonState();
}

class _AwaitableIconButtonState extends State<AwaitableIconButton> {
  var _isExecuting = false;

  @override
  Widget build(BuildContext context) {
    return IconButton(
      onPressed: widget.onPressed == null ? null : _onPressed,
      icon: AnimatedSwitcher(
        duration: const Duration(milliseconds: 200),
        child: _isExecuting
            ? widget.indicatorWidget ??
                const CircularProgressIndicator()
            : widget.icon,
      ),
    );
  }

  Future<void> _onPressed() async {
    if (_isExecuting) {
      // ボタンアクション実行中は何もしない（連打防止）
      return;
    }
    setState(() => _isExecuting = true);
    await widget.onPressed!.call();
    // 画面遷移先から戻ってきた時等のために存在確認してから実行
    if (mounted) {
      setState(() => _isExecuting = false);
    }
  }
}

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

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

class MyHomePage extends StatefulWidget {
  final String title;

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

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: AwaitableIconButton(
          onPressed: () async {
            print('start');
            await Future<void>.delayed(const Duration(seconds: 3));
            print('end');
          },
          icon:const Icon(Icons.send),
        ),
      ),
    );
  }
}