习惯追踪器：打卡一天

本课属于 Coddy Flutter 学习旅程的“项目”单元。第 30 课，共 36 课。

点按一个圆圈即可勾选当天，再次点按即可取消勾选。习惯数据保存在屏幕的状态中，但圆圈是在 HabitCard 深处绘制的。点按操作必须传到数据所在的位置。

这就是通过回调向上提升状态。屏幕负责管理更改：

void _toggle(Habit habit, int day) {
  setState(() {
    habit.days[day] = !habit.days[day];
  });
}

它会给每张卡片传入一个函数：onToggle: (day) => _toggle(habit, day)。卡片中该函数的类型是 void Function(int day)，它接收当天的编号。每个圆圈都会获得一个普通的 VoidCallback：onTap: () => onToggle(i)，并用会调用它的 GestureDetector 包裹其 Container。

!habit.days[day] 会翻转一个 bool 值：true 会变成 false，反之亦然，因此一个函数就能同时完成勾选和取消勾选。

挑战

困难

勾选日期：

在屏幕的状态中添加 _toggle 方法
为 HabitCard 添加一个必需的 onToggle，类型为 void Function(int day)，并传入 (day) => _toggle(habit, day)
为 DayCircle 添加一个必需的 VoidCallback onTap，用 GestureDetector 包裹它的 Container，并传入 () => onToggle(i)

亲手试试

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.green),
      ),
      home: const HabitScreen(),
    );
  }
}

const List<String> dayNames = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];

class Habit {
  Habit(this.name, this.days);

  final String name;
  final List<bool> days;
}

class HabitScreen extends StatefulWidget {
  const HabitScreen({super.key});

  @override
  State<HabitScreen> createState() => _HabitScreenState();
}

class _HabitScreenState extends State<HabitScreen> {
  final List<Habit> _habits = [
    Habit('Drink water', [true, true, true, false, true, false, false]),
    Habit('Read 10 pages', [true, false, true, true, false, false, false]),
    Habit('Stretch', List.filled(7, false)),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Habits')),
      body: ListView(
        padding: const EdgeInsets.fromLTRB(16, 8, 16, 88),
        children: [
          for (Habit habit in _habits) HabitCard(habit: habit),
        ],
      ),
    );
  }
}

class HabitCard extends StatelessWidget {
  const HabitCard({super.key, required this.habit});

  final Habit habit;

  @override
  Widget build(BuildContext context) {
    final textTheme = Theme.of(context).textTheme;
    return Card(
      margin: const EdgeInsets.only(top: 12),
      clipBehavior: Clip.antiAlias,
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(habit.name, style: textTheme.titleMedium),
            const SizedBox(height: 12),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                for (int i = 0; i < 7; i++) DayCircle(label: dayNames[i], done: habit.days[i]),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

class DayCircle extends StatelessWidget {
  const DayCircle({super.key, required this.label, required this.done});

  final String label;
  final bool done;

  @override
  Widget build(BuildContext context) {
    final colors = Theme.of(context).colorScheme;
    return Container(
      width: 40,
      height: 40,
      alignment: Alignment.center,
      decoration: BoxDecoration(
        shape: BoxShape.circle,
        color: done ? colors.primary : colors.surfaceContainerHighest,
      ),
      child: Text(
        label,
        style: TextStyle(
          fontSize: 11,
          fontWeight: FontWeight.bold,
          color: done ? colors.onPrimary : colors.onSurfaceVariant,
        ),
      ),
    );
  }
}