From local flutter/flutter repo, `git checkout -b shihaohong-toggle-button master`, then `git pull https://github.com/shihaohong/flutter.git toggle-button`

toggle_buttons.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'ToggleButtons Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: ToggleButtonPlayground(title: 'ToggleButtons Demo Page'),
    );
  }
}

class ToggleButtonPlayground extends StatefulWidget {
  ToggleButtonPlayground({Key key, this.title}) : super(key: key);

  final String title;

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

class _ToggleButtonPlaygroundState extends State<ToggleButtonPlayground> {
  List<bool> isSelected = [
    true,
    false,
    true,
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ToggleButtonsTheme(
        child: Center(
          child: ToggleButtons(
            children: <Widget>[
              Icon(Icons.ac_unit),
              Icon(Icons.call),
              Icon(Icons.cake),
            ],
            onPressed: (int index) {
              setState(() {
                isSelected[index] = !isSelected[index];
              });
            },
            isSelected: isSelected,
          ),
        ),
      ),
    );
  }
}