习惯追踪器：浅色与深色

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

人们常在深夜查看习惯，因此最后一个功能是深色模式，顶部栏上有一个按钮：点击月亮图标开启，再点击太阳图标切回浅色模式。

主题设置在 MaterialApp 中，所以切换功能也放在那里：让 MyApp 变成一个带有 bool _dark 的 StatefulWidget。给 MaterialApp 设置两种主题，再通过 themeMode 选择其中一种：

darkTheme: ThemeData(
  colorScheme: ColorScheme.fromSeed(
    seedColor: Colors.green,
    brightness: Brightness.dark,
  ),
),
themeMode: _dark ? ThemeMode.dark : ThemeMode.light,

按钮位于习惯屏幕中，距离 MyApp 很远。再把状态提升一层：给 HabitScreen 添加 dark 来选择图标，并添加一个要调用的 onToggleTheme 回调。屏幕通过 widget.dark 和 widget.onToggleTheme 从自身的 widget 中读取它们。

应用中的所有颜色都来自主题，所以卡片、圆圈和环形图都会随主题切换。你的习惯仍会保持勾选状态，因为它们保存在屏幕的状态中，而不是主题中。

这是本课程项目的最后一课。检查会使用完整的习惯追踪器：添加、勾选、连续记录、删除、环形图和深色模式。

挑战

困难

添加深色模式：

让 MyApp 成为一个 StatefulWidget，并设置 bool _dark = false；为 MaterialApp 添加一个基于相同绿色种子创建的 darkTheme，其中包含 Brightness.dark，再根据 _dark 设置 themeMode
为 HabitScreen 添加必需的 bool dark 和 VoidCallback onToggleTheme；MyApp 传入 _dark，以及一个在 setState 中切换它的函数
在顶部栏的 actions 中，添加一个 IconButton，使它在浅色模式下显示 Icons.dark_mode，在深色模式下显示 Icons.light_mode，并调用 widget.onToggleTheme

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;

  int get done => days.where((day) => day).length;

  int get streak {
    int best = 0;
    int run = 0;
    for (bool day in days) {
      if (day) {
        run++;
        if (run > best) best = run;
      } else {
        run = 0;
      }
    }
    return best;
  }
}

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)),
  ];

  int get _ticks => _habits.fold(0, (sum, habit) => sum + habit.done);
  int get _possible => _habits.length * 7;

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

  Future<void> _addHabit() async {
    String name = '';
    final added = await showDialog<bool>(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('New habit'),
        content: TextField(
          autofocus: true,
          decoration: const InputDecoration(labelText: 'Habit name'),
          onChanged: (value) => name = value,
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context, false),
            child: const Text('Cancel'),
          ),
          FilledButton(
            onPressed: () => Navigator.pop(context, true),
            child: const Text('Add'),
          ),
        ],
      ),
    );
    if (added != true || name.trim().isEmpty) return;
    setState(() {
      _habits.add(Habit(name.trim(), List.filled(7, false)));
    });
  }

  Future<void> _deleteHabit(Habit habit) async {
    final delete = await showDialog<bool>(
      context: context,
      builder: (context) => AlertDialog(
        title: Text('Delete ${habit.name}?'),
        content: const Text('Its ticks for this week go with it.'),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context, false),
            child: const Text('Cancel'),
          ),
          FilledButton(
            onPressed: () => Navigator.pop(context, true),
            child: const Text('Delete'),
          ),
        ],
      ),
    );
    if (delete != true) return;
    setState(() {
      _habits.remove(habit);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Habits')),
      floatingActionButton: FloatingActionButton(
        onPressed: _addHabit,
        child: const Icon(Icons.add),
      ),
      body: ListView(
        padding: const EdgeInsets.fromLTRB(16, 8, 16, 88),
        children: [
          ProgressCard(ticks: _ticks, possible: _possible),
          for (Habit habit in _habits)
            HabitCard(
              habit: habit,
              onToggle: (day) => _toggle(habit, day),
              onLongPress: () => _deleteHabit(habit),
            ),
        ],
      ),
    );
  }
}

class ProgressCard extends StatelessWidget {
  const ProgressCard({super.key, required this.ticks, required this.possible});

  final int ticks;
  final int possible;

  @override
  Widget build(BuildContext context) {
    final colors = Theme.of(context).colorScheme;
    final textTheme = Theme.of(context).textTheme;
    final progress = possible == 0 ? 0.0 : ticks / possible;
    return Card(
      margin: EdgeInsets.zero,
      color: colors.primaryContainer,
      child: Padding(
        padding: const EdgeInsets.all(20),
        child: Row(
          children: [
            SizedBox(
              width: 72,
              height: 72,
              child: Stack(
                fit: StackFit.expand,
                children: [
                  CircularProgressIndicator(
                    value: progress,
                    strokeWidth: 8,
                    strokeCap: StrokeCap.round,
                    backgroundColor: colors.surface,
                  ),
                  Center(
                    child: Text(
                      '${(progress * 100).round()}%',
                      style: textTheme.titleMedium?.copyWith(fontWeight: FontWeight.bold),
                    ),
                  ),
                ],
              ),
            ),
            const SizedBox(width: 20),
            Expanded(
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text('This week', style: textTheme.titleLarge),
                  const SizedBox(height: 4),
                  Text('$ticks of $possible ticks'),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

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

  final Habit habit;
  final void Function(int day) onToggle;
  final VoidCallback onLongPress;

  @override
  Widget build(BuildContext context) {
    final textTheme = Theme.of(context).textTheme;
    return Card(
      margin: const EdgeInsets.only(top: 12),
      clipBehavior: Clip.antiAlias,
      child: InkWell(
        onLongPress: onLongPress,
        child: Padding(
          padding: const EdgeInsets.all(16),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Row(
                children: [
                  Expanded(child: Text(habit.name, style: textTheme.titleMedium)),
                  Text('${habit.done} of 7 days', style: textTheme.bodySmall),
                ],
              ),
              const SizedBox(height: 12),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  for (int i = 0; i < 7; i++)
                    DayCircle(
                      label: dayNames[i],
                      done: habit.days[i],
                      onTap: () => onToggle(i),
                    ),
                ],
              ),
              const SizedBox(height: 12),
              Row(
                children: [
                  Icon(
                    Icons.local_fire_department,
                    size: 20,
                    color: habit.streak > 0 ? Colors.orange : Theme.of(context).colorScheme.outline,
                  ),
                  const SizedBox(width: 4),
                  Text(habit.streak == 0 ? 'No streak yet' : '${habit.streak} day streak'),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}

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

  final String label;
  final bool done;
  final VoidCallback onTap;

  @override
  Widget build(BuildContext context) {
    final colors = Theme.of(context).colorScheme;
    return GestureDetector(
      onTap: onTap,
      child: 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,
          ),
        ),
      ),
    );
  }
}