web43 todo list 追加画面

• debugShowCheckedModeBanner: false　デバッグモードでは指定しないとバナー非表示にできない（リリースモードではデフォルトで非表示）
• home: TodoListPage()　StetelessWidget に StetefulWidget を載せる

import 'package:flutter/material.dart';

void main() => runApp(const MyTodoApp());

class MyTodoApp extends StatelessWidget
{
  const MyTodoApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context)
  {
    return MaterialApp
    (
      debugShowCheckedModeBanner: false,
      title: 'My Todo App',
      theme: ThemeData(primarySwatch: Colors.blue, visualDensity: VisualDensity.adaptivePlatformDensity),
      home: TodoListPage(),
    );
  }
}

// リスト一覧画面用Widget
class TodoListPage extends StatefulWidget {
  @override
  _TodoListPageState createState() => _TodoListPageState();
}

class _TodoListPageState extends State<TodoListPage> {
  // Todoリストのデータ
  List<String> todoList = [];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // AppBarを表示し、タイトルも設定
      appBar: AppBar(
        title: Text('リスト一覧'),
      ),
      // データを元にListViewを作成
      body: ListView.builder(
        itemCount: todoList.length,
        itemBuilder: (context, index) {
          return Card(
            child: ListTile(
              title: Text(todoList[index]),
            ),
          );
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () async {
          // "push"で新規画面に遷移
          // リスト追加画面から渡される値を受け取る
          final newListText = await Navigator.of(context).push(
            MaterialPageRoute(builder: (context) {
              // 遷移先の画面としてリスト追加画面を指定
              return TodoAddPage();
            }),
          );
          if (newListText != null) {
            // キャンセルした場合は newListText が null となるので注意
            setState(() {
              // リスト追加
              todoList.add(newListText);
            });
          }
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

class TodoAddPage extends StatefulWidget {
  @override
  _TodoAddPageState createState() => _TodoAddPageState();
}

class _TodoAddPageState extends State<TodoAddPage> {
  // 入力されたテキストをデータとして持つ
  String _text = '';

  // データを元に表示するWidget
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('リスト追加'),
      ),
      body: Container(
        // 余白を付ける
        padding: EdgeInsets.all(64),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            // 入力されたテキストを表示
            Text(_text, style: TextStyle(color: Colors.blue)),
            const SizedBox(height: 8),
            // テキスト入力
            TextField(
              // 入力されたテキストの値を受け取る（valueが入力されたテキスト）
              onChanged: (String value) {
                // データが変更したことを知らせる（画面を更新する）
                setState(() {
                  // データを変更
                  _text = value;
                });
              },
            ),
            const SizedBox(height: 8),
            Container(
              // 横幅いっぱいに広げる
              width: double.infinity,
              // リスト追加ボタン
              child: ElevatedButton(
                onPressed: () {
                  // "pop"で前の画面に戻る
                  // "pop"の引数から前の画面にデータを渡す
                  Navigator.of(context).pop(_text);
                },
                child: Text('リスト追加', style: TextStyle(color: Colors.white)),
              ),
            ),
            const SizedBox(height: 8),
            Container(
              // 横幅いっぱいに広げる
              width: double.infinity,
              // キャンセルボタン
              child: TextButton(
                // ボタンをクリックした時の処理
                onPressed: () {
                  // "pop"で前の画面に戻る
                  Navigator.of(context).pop();
                },
                child: Text('キャンセル'),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

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

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          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),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}