todostate.dart

/// State is composed all the variables declared in the State implementation of a Stateful widget
class TodoListState extends State<TodoList> {
  final List<Todo> todos = List<Todo>();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Todo'),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: todos.length > 0
            ? ListView.builder(
                itemCount: todos.length,
                itemBuilder: _buildRow,
              )
            : Text('There is nothing here yet. Start by adding some Todos'),
      ),
    );
  }

  /// build a single row of the list
  Widget _buildRow(context, index) => Row(
        children: <Widget>[
          Checkbox(
              value: todos[index].completed,
              onChanged: (value) => _changeTodo(index, value)),
          Text(todos[index].label,
              style: TextStyle(
                  decoration: todos[index].completed
                      ? TextDecoration.lineThrough
                      : null))
        ],
      );

  /// toggle the completed state of a todo item
  _changeTodo(int index, bool value) =>
      setState(() => todos[index].completed = value);
}