todo list app using stateful widget

todo_stateful.dart

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

// bloc & get packages 
// behind

void main() {
  runApp(MyApp());
  // expects to receive a widget and mount it as a root widget
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // CuprtinoApp
      theme: ThemeData(
        primarySwatch: Colors.purple,
      ),
      debugShowCheckedModeBanner: false,
//       home: TodoList(), // '/',
      routes: {
        '/': (context) => TodoList()
      },
    );
  }
}

class Todo {
  final int id;
  final String text;
  final bool isCompleted;

  Todo({required this.id, required this.text, required this.isCompleted});

  Todo.initialize({String? text})
      : id = DateTime.now().microsecondsSinceEpoch,
        text = text ?? '',
        isCompleted = false;
  
  Todo copyWith({int? id, String? text, bool? isCompleted}) {
    return Todo(
      id: id ?? this.id,
      text: text ?? this.text,
      isCompleted: isCompleted ?? this.isCompleted,
    );
  }

  @override
  String toString() {
    return {'id': id, 'text': text, 'isCompleted': isCompleted}.toString();
  }
}

class TodoCard extends StatelessWidget {
  final Todo todo;
  final void Function(Todo todo)? deleteTodo, checkTodo; // (Todo todo) {}

  const TodoCard({required this.todo, this.deleteTodo, this.checkTodo});

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Checkbox(
          onChanged: (bool? state) {
            checkTodo!(todo);
          },
          value: todo.isCompleted,
        ), // null disable checkbox
        Expanded(child: Text(todo.text)), // flex: 1
        IconButton(
          icon: const Icon(Icons.delete),
          onPressed: () => deleteTodo!(todo),
        ),
      ],
    );
  }
}

class TodoList extends StatefulWidget {
  // @immutable
  final String name = 'Todos';

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

class TodoListState extends State<TodoList> {
  // 1. createState() // invoked only once
  // 2. initState() // invoked only once
  // 3. didChangeDependencies()
  // 4. build()
  // 5. didUpdateWidget()
  // 6. dispose() // invoked only once, when widget is removed from the tree
  
  // streams

  final textController = TextEditingController();
  List<Todo> todos = [];

  void addTodo() {
    final text = textController.text;
    if (text.isEmpty) return;
    setState(() => todos.add(Todo.initialize(text: text))); // todo 
    textController.clear();
  }

  void deleteTodo(Todo todo) {
    setState(() => todos.remove(todo));
  }
  
  void checkTodo(Todo todo) {
    final index = todos.indexOf(todo);
    setState(() => todos[index] = todo.copyWith(isCompleted: !todo.isCompleted));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.name)),
      body: Column(
        children: [
          Row(
            children: [
              Expanded(
                child: TextField(
                  controller: textController,
                  decoration: const InputDecoration(
                    contentPadding: EdgeInsets.all(16),
                    border: InputBorder.none,
                  ),
                ),
              ),
              TextButton(
                child: const Text('Save'),
                onPressed: addTodo,
              ),
            ],
          ),
          const Divider(color: Colors.purple, height: 0),
          Expanded(
            child: ListView(
              children: todos
                  .map((todo) => TodoCard(todo: todo, deleteTodo: deleteTodo, checkTodo: checkTodo))
                  .toList(),
            ),
          )
        ],
      ),
    );
  }
}