【 Flutter 】Flutter を 基礎 から 学習 ( ウィジェット編 ) part107 Async

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
//intl: ^0.17.0
import 'package:intl/intl.dart';

void main() {
  // runApp(new MaterialApp(home: new MyApp()));
  runApp(new MaterialApp(home: new SamplePage()));
}

class SamplePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _SampleState();
  }
}

class _SampleState extends State<SamplePage> {
  _toDateTime(TimeOfDay t) {
    var now = DateTime.now();
    return DateTime(now.year, now.month, now.day, t.hour, t.minute);
  }

  bool _init = true;
  late DateTime _time = DateTime.now(); // late? これはなんでしょうか？

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Container(
          decoration: BoxDecoration(
            border: Border(
              bottom: BorderSide(width: 3),
            ),
          ),
          child: Text(
            _init ? "未選択" : DateFormat('hh:mm a').format(_time),
            style: TextStyle(fontSize: 50),
          ),
        ),
        ElevatedButton(
          child: Text(
            "時刻を選択する",
            style: TextStyle(fontSize: 20),
          ),
          style: ElevatedButton.styleFrom(
            primary: Colors.deepOrangeAccent, //ボタンの背景色
          ),
          onPressed: () async {
            final select = await showTimePicker(
              context: context,
              initialTime: TimeOfDay.now(),
            );
            this.setState(() => _time = _toDateTime(select!));
            this.setState(() {
              _time = _toDateTime(select!);
              _init = false;
            });
          },
        ),
      ],
    );
  }
}