main.dart

import 'package:flutter/material.dart';

class BasicAppBarSample extends StatefulWidget {
  @override
  _BasicAppBarSampleState createState() => _BasicAppBarSampleState();
}

class _BasicAppBarSampleState extends State<BasicAppBarSample> {
  Choice _selectedChoice = choices[0];

  void _select(Choice choice) {
    setState(() {
      _selectedChoice = choice;
    });
  }

  @override
  Widget build(BuildContext context) {
    const double windowPaddingTop = 24;
    double mediaQueryTop;

    return MediaQuery(
      data: const MediaQueryData(
        padding: EdgeInsets.only(top: windowPaddingTop),
      ),
      child: Builder(builder: (BuildContext context) {
        mediaQueryTop = MediaQuery.of(context).padding.top;
        print(mediaQueryTop);
        return MaterialApp(
          home: Padding(
            padding: EdgeInsets.only(top: mediaQueryTop),
            child: Scaffold(
              appBar: AppBar(
                title: const Text('Basic AppBar'),
                actions: <Widget>[
                  IconButton(
                    icon: Icon(choices[0].icon),
                    onPressed: () {
                      _select(choices[0]);
                    },
                  ),
                  IconButton(
                    icon: Icon(choices[1].icon),
                    onPressed: () {
                      _select(choices[1]);
                    },
                  ),
                  PopupMenuButton<Choice>(
                    onSelected: _select,
                    initialValue: _selectedChoice, // initialValue added
                    itemBuilder: (BuildContext context) {
                      return choices
                          .skip(2)
                          .map<PopupMenuItem<Choice>>((Choice choice) {
                        return PopupMenuItem<Choice>(
                          value: choice,
                          child: Text(choice.title),
                        );
                      }).toList();
                    },
                  ),
                ],
              ),
              body: Padding(
                padding: const EdgeInsets.all(16.0),
                child: ChoiceCard(choice: _selectedChoice),
              ),
            ),
          ),
        );
      }),
    );
  }
}

class Choice {
  const Choice({this.title, this.icon});
  final String title;
  final IconData icon;
}

const List<Choice> choices = <Choice>[
  Choice(title: 'Car', icon: Icons.directions_car),
  Choice(title: 'Bicycle', icon: Icons.directions_bike),
  Choice(title: 'Boat', icon: Icons.directions_boat),
  Choice(title: 'Bus', icon: Icons.directions_bus),
  Choice(title: 'Train', icon: Icons.directions_railway),
  Choice(title: 'Walk', icon: Icons.directions_walk),
];

class ChoiceCard extends StatelessWidget {
  const ChoiceCard({Key key, this.choice}) : super(key: key);

  final Choice choice;

  @override
  Widget build(BuildContext context) {
    final TextStyle textStyle = Theme.of(context).textTheme.headline4;
    return Card(
      color: Colors.white,
      child: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Icon(choice.icon, size: 128.0, color: textStyle.color),
            Text(choice.title, style: textStyle),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(home: BasicAppBarSample()));
}