[Creating Stateful Widgets] #flutter #dart #stateful #widget

flutter_statefull_widget.dart

class CategoryRoute extends StatefulWidget {
  const CategoryRoute();

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

class _CategoryRouteState extends State<CategoryRoute> {
  final _categories = <Category>[];

  static const _categoryNames = <String>[
    'Length',
    'Area',
    'Volume',
    'Mass',
    'Time',
    'Digital Storage',
    'Energy',
    'Currency',
  ];

  static const _baseColors = <Color>[
    Colors.teal,
    Colors.orange,
    Colors.pinkAccent,
    Colors.blueAccent,
    Colors.yellow,
    Colors.greenAccent,
    Colors.purpleAccent,
    Colors.red,
  ];

  @override
  void initState() {
    super.initState();
    for (var i = 0; i < _categoryNames.length; i++) {
      _categories.add(Category(
        name: _categoryNames[i],
        color: _baseColors[i],
        iconLocation: Icons.cake,
        units: _retrieveUnitList(_categoryNames[i]),
      ));
    }
  }

  Widget _buildCategoryWidgets() {
    return ListView.builder(
      itemBuilder: (BuildContext context, int index) => _categories[index],
      itemCount: _categories.length,
    );
  }

  List<Unit> _retrieveUnitList(String categoryName) {
    return List.generate(10, (int i) {
      i += 1;
      return Unit(
        name: '$categoryName Unit $i',
        conversion: i.toDouble(),
      );
    });
  }

  @override
  Widget build(BuildContext context) {
    final listView = Container(
      color: _backgroundColor,
      padding: EdgeInsets.symmetric(horizontal: 8.0),
      child: _buildCategoryWidgets(),
    );

    final appBar = AppBar(
      elevation: 0.0,
      title: Text(
        'Unit Converter',
        style: TextStyle(
          color: Colors.black,
          fontSize: 30.0,
        ),
      ),
      centerTitle: true,
      backgroundColor: _backgroundColor,
    );

    return Scaffold(
      appBar: appBar,
      body: listView,
    );
  }
}

flutter_statefull_widget_listview.dart

class $2 extends State<$1> {
  final p1 = <T1>[];
  
  const $2();
  static const _listValues1 = <String>[
    'v1',
    'v2',
    'v3',
  ];
  
  @override
  void initState() {
    super.initState();
    for (var i = 0; i < _listValues1.length; i++) {
      p1.add(T1(value: _listValues1[i]));
    }
  }
  
  _buildP1Widgets(List<Widget> p1) {
    return ListView.builder(
          itemBuilder: (BuildContext context, int index) => p1[index],
          itemCount: p1.length,
        );
  }
  
  Widget build(BuildContext context) {
      return Container(
                  padding: EdgeInsets.symmetric(horizontal: 8.0),
                  child: _buildP1Widgets(p1),
                 );
  }
}

flutter_widget_listitem.dart

class T1 extends StatelessWidget {
  final T1 v1;
  
  const $1({
    Key key,
    @required this.v1,
  }) : assert( v1 != null ),
       super(key: key);
  
  @override
  Widget build(BuildContext context) {
    return Widget();
  }
}