todotxt_reminder/lib/task_item.dart

import 'package:flutter/material.dart';

class TaskItem extends StatefulWidget {

  final bool? done;

  const TaskItem({super.key, this.done});

  @override
  State<TaskItem> createState() => _TaskItemState();
}

class _TaskItemState extends State<TaskItem>{

  bool? _done;

  @override
  void initState() {
    super.initState();
    _done = widget.done;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      width: 60.0,
      height: 60.0,
      decoration: BoxDecoration(border: Border(
          left: BorderSide(color: Theme.of(context).colorScheme.background, width: 1)
      ),),
      margin: const EdgeInsets.all(0.0),
      child: _done == null ? null : Checkbox(value: _done, onChanged: (newState) => setState(() {
        _done = newState!;
      })),
    );
  }
}