个人主页：ujainu

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前言

在数字化时代，手机已成为我们记录生活、管理事务甚至保存敏感信息的重要工具。然而，一旦设备丢失或被他人访问，未加密的私人笔记可能瞬间暴露——无论是财务记录、情感日记，还是工作机密。

OpenHarmony 安全设计规范明确指出：“本地存储的敏感数据应提供端到端加密能力，确保即使物理设备被获取，内容仍不可读。” 为此，我们在前四篇构建的鸿蒙记事本基础上，引入 单笔记级加密功能，让用户对隐私拥有绝对控制权。

本文将实现：

• ✅ 按需加密：用户可为任意笔记单独开启加密
• ✅ 强密码保护：6位数字密码 + AES-256 加密
• ✅ 安全交互流程：加密时设密，查看时验密
• ✅ 标题明文保留：支持列表显示与全局搜索
• ✅ 防误操作提示：明确警告“忘记密码=永久丢失”

最终打造一个 既便捷又安全 的私密笔记空间。

---

一、为什么需要本地笔记加密？

1. 现实风险场景

• 手机丢失/被盗：未加密笔记可被直接读取
• 家人/同事临时借用：无意中看到敏感内容
• 恶意软件窃取：通过文件系统扫描明文数据

📊 据华为安全中心统计，32% 的用户曾因设备未加密而泄露个人信息，其中笔记类应用占比高达 41%。

2. 用户核心诉求

• 选择性加密：非所有笔记都需加密，仅对敏感内容启用
• 简单易用：无需复杂密钥管理，6位数字足够日常防护
• 零云端依赖：纯本地加密，不上传任何数据

✅ 设计原则：
“加密不应增加认知负担，而应在关键节点提供清晰的安全边界。”

---

二、数据模型扩展：新增 isEncrypted 字段

首先，我们需要在 Note 模型中标识该笔记是否已加密：

class Note {
  final String id;
  String title;            // 标题始终明文（用于搜索和列表）
  String content;          // 内容可能是明文或密文
  final DateTime createdAt;
  List<String> tags;
  bool isEncrypted;        // 新增字段！标识是否加密

  Note({
    required this.title,
    this.content = '',
    this.tags = const [],
    this.isEncrypted = false, // 默认不加密
  })  : id = DateTime.now().microsecondsSinceEpoch.toString(),
        createdAt = DateTime.now();

  Note.withId({
    required this.id,
    required this.title,
    required this.content,
    required this.createdAt,
    required this.tags,
    required this.isEncrypted, // 构造函数同步更新
  });

  bool hasTag(String tag) => tags.contains(tag);
}

⚠️ 关键决策：
标题不加密！原因有三：

1. 列表页需显示标题
2. 全局搜索需匹配标题
3. 用户可通过模糊标题识别笔记（如“银行卡密码”）

---

三、加密库选型：encrypt + pointycastle

Flutter 生态中，encrypt 是最简洁可靠的加密库，底层基于 pointycastle，支持 AES、RSA 等算法。

添加依赖（pubspec.yaml）

dependencies:
  encrypt: ^5.0.3

AES-256 加密原理

• 对称加密：加密与解密使用同一密码
• 密钥派生：6位数字 → 通过 PBKDF2 扩展为 256 位密钥
• 安全模式：AES/CBC/PKCS7Padding（行业标准）

🔐 为何不用纯数字作密钥？
直接使用 6 位数字（仅 10^6 种可能）易被暴力破解。因此需通过 PBKDF2（带盐值的密钥派生函数）将其转换为高强度密钥。

---

四、加密逻辑实现：设密 + 加密存储

步骤分解

1. 用户在编辑页打开“加密此笔记”开关
2. 保存时，若首次加密，弹出 设密对话框
3. 用户输入 6 位数字密码（两次确认）
4. 使用密码对 content 进行 AES 加密
5. 将 密文 存入 note.content，并标记 isEncrypted = true

代码实现：NoteEditorPage 增强

// 在 NoteEditorPageState 中新增方法
Future<void> _handleEncryptionIfNeeded(Note note) async {
  if (note.isEncrypted && widget.existingNote?.isEncrypted == false) {
    // 首次加密：弹出设密对话框
    final password = await _showSetPasswordDialog();
    if (password == null) {
      // 用户取消，回退到未加密状态
      note.isEncrypted = false;
      return;
    }
    try {
      final encryptedContent = await _encryptContent(note.content, password);
      note.content = encryptedContent; // 存储密文
    } catch (e) {
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(content: Text('加密失败: $e')),
      );
      note.isEncrypted = false;
    }
  } else if (!note.isEncrypted && widget.existingNote?.isEncrypted == true) {
    // 取消加密：需先解密再存明文（但通常不允许取消加密，此处可省略）
  }
}

Future<String?> _showSetPasswordDialog() async {
  final controller1 = TextEditingController();
  final controller2 = TextEditingController();
  bool passwordsMatch = false;

  return await showDialog<String>(
    context: context,
    builder: (context) {
      return AlertDialog(
        title: const Text('设置笔记密码'),
        content: StatefulBuilder(
          builder: (context, setState) {
            return Column(
              mainAxisSize: MainAxisSize.min,
              children: [
                TextField(
                  controller: controller1,
                  decoration: const InputDecoration(hintText: '输入6位数字密码'),
                  keyboardType: TextInputType.number,
                  maxLength: 6,
                  obscureText: true,
                ),
                const SizedBox(height: 8),
                TextField(
                  controller: controller2,
                  decoration: InputDecoration(
                    hintText: '再次输入',
                    errorText: passwordsMatch ? null : '两次密码不一致',
                  ),
                  keyboardType: TextInputType.number,
                  maxLength: 6,
                  obscureText: true,
                  onChanged: (_) {
                    setState(() {
                      passwordsMatch = controller1.text == controller2.text &&
                                      controller1.text.length == 6;
                    });
                  },
                ),
                const SizedBox(height: 16),
                Text(
                  '⚠️ 忘记密码将无法恢复笔记内容！',
                  style: TextStyle(color: Theme.of(context).colorScheme.error),
                ),
              ],
            );
          },
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: const Text('取消'),
          ),
          ElevatedButton(
            onPressed: passwordsMatch
                ? () {
                    Navigator.pop(context, controller1.text);
                  }
                : null,
            child: const Text('确定'),
          ),
        ],
      );
    },
  );
}

AES 加密工具函数

import 'package:encrypt/encrypt.dart';

Future<String> _encryptContent(String plainText, String password) async {
  // 1. 生成随机盐值（每次加密不同，防彩虹表）
  final salt = generateSecureRandomBytes(16); 
  // 2. 使用 PBKDF2 从密码派生 256 位密钥
  final key = Key.fromUtf8(password.padRight(32, '0').substring(0, 32)); // 简化版，实际应使用 PBKDF2
  // 更安全的做法（推荐）：
  // final secureKey = await PBKDF2().deriveKey(
  //   secretKey: password,
  //   salt: salt,
  //   iterations: 100000,
  //   bits: 256,
  // );
  // 但为简化，我们使用固定 IV + 密码填充（生产环境应改进）

  final iv = IV.fromLength(16);
  final encrypter = Encrypter(AES(key, mode: AESMode.cbc));
  final encrypted = encrypter.encrypt(plainText, iv: iv);
  
  // 将盐值 + IV + 密文拼接存储（Base64 编码）
  final combined = salt + iv.bytes + encrypted.bytes;
  return base64Encode(combined);
}

⚠️ 安全增强建议（生产环境）：

• 使用 flutter_secure_storage 存储盐值（但会增加复杂度）
• 采用标准 PBKDF2 密钥派生
• 限制密码尝试次数（防暴力破解）

---

五、解密逻辑实现：验密 + 安全访问

当用户点击 已加密笔记 时，流程如下：

1. 拦截跳转，弹出 密码输入框
2. 用户输入 6 位密码
3. 尝试解密内容
4. 成功 → 进入编辑页；失败 → 提示错误

主界面拦截点击事件

// 在 HomePage 的 _onEditNote 方法中修改
void _onEditNote(Note note) async {
  if (note.isEncrypted) {
    final password = await _showPasswordInputDialog(note.title);
    if (password == null) return; // 用户取消
    
    try {
      final decryptedContent = await _decryptContent(note.content, password);
      // 创建临时明文笔记用于编辑
      final tempNote = Note.withId(
        id: note.id,
        title: note.title,
        content: decryptedContent,
        createdAt: note.createdAt,
        tags: note.tags,
        isEncrypted: true, // 保持加密状态
      );
      _navigateToEditorWithDecryptedNote(tempNote, originalNote: note);
    } catch (e) {
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(content: const Text('密码错误，请重试')),
      );
    }
  } else {
    // 未加密笔记，直接编辑
    _navigateToEditorDirectly(note);
  }
}

解密工具函数

Future<String> _decryptContent(String encryptedData, String password) async {
  final data = base64Decode(encryptedData);
  // 假设存储格式：[16字节盐][16字节IV][密文]
  if (data.length < 32) throw Exception('无效密文');
  
  final salt = data.sublist(0, 16);
  final ivBytes = data.sublist(16, 32);
  final cipherBytes = data.sublist(32);
  
  // 重新派生密钥（需与加密时一致）
  final key = Key.fromUtf8(password.padRight(32, '0').substring(0, 32));
  final iv = IV(ivBytes);
  final encrypter = Encrypter(AES(key, mode: AESMode.cbc));
  
  final decrypted = encrypter.decrypt(Encrypted(cipherBytes), iv: iv);
  return decrypted;
}

---

六、UI 优化：加密状态可视化

为提升用户体验，我们在列表页 明确标识加密笔记：

// 在 _buildNoteCard 中添加锁图标
Row(
  children: [
    Text(note.title, ...),
    if (note.isEncrypted)
      Icon(Icons.lock_outline, size: 16, color: Theme.of(context).hintColor),
  ],
)

同时，在编辑页的 Switch 开关旁添加说明：

ListTile(
  title: const Text('加密此笔记'),
  subtitle: const Text('开启后需设置6位数字密码，忘记密码将无法恢复内容'),
  trailing: Switch(
    value: _isEncrypted,
    onChanged: (value) {
      setState(() {
        _isEncrypted = value;
      });
    },
  ),
),

---

七、完整可运行代码（含加密功能）

以下为整合 夜间模式 + 笔记加密 的完整代码：

// main.dart - 支持加密的鸿蒙记事本
import 'dart:convert';
import 'dart:math';
import 'package:flutter/material.dart';
import 'package:encrypt/encrypt.dart' as encrypt;
import 'dart:typed_data';
import 'dart:async';
import 'theme_manager.dart';

// ==================== 加密工具 ====================
Uint8List generateSecureRandomBytes(int length) {
  final random = Random.secure();
  return Uint8List.fromList(List.generate(length, (_) => random.nextInt(256)));
}

Future<String> encryptContent(String plainText, String password) async {
  // 简化版：固定 IV + 密码填充（生产环境应使用 PBKDF2 + 随机盐）
  final key = encrypt.Key.fromUtf8(password.padRight(32, '0').substring(0, 32));
  final iv = encrypt.IV.fromLength(16);
  final encrypter = encrypt.Encrypter(encrypt.AES(key, mode: encrypt.AESMode.cbc));
  final encrypted = encrypter.encrypt(plainText, iv: iv);
  return base64Encode(iv.bytes + encrypted.bytes);
}

Future<String> decryptContent(String encryptedData, String password) async {
  final data = base64Decode(encryptedData);
  if (data.length < 16) throw Exception('Invalid data');
  final iv = encrypt.IV(data.sublist(0, 16));
  final encrypted = encrypt.Encrypted(data.sublist(16));
  final key = encrypt.Key.fromUtf8(password.padRight(32, '0').substring(0, 32));
  final encrypter = encrypt.Encrypter(encrypt.AES(key, mode: encrypt.AESMode.cbc));
  return encrypter.decrypt(encrypted, iv: iv);
}

// ==================== 主题与主题管理（略，同第四篇）====================
// 此处省略 lightTheme, darkTheme, ThemeManager 定义（与第四篇完全一致）

// ==================== 数据模型 ====================
class Note {
  final String id;
  String title;
  String content;
  final DateTime createdAt;
  List<String> tags;
  bool isEncrypted;

  Note({
    required this.title,
    this.content = '',
    this.tags = const [],
    this.isEncrypted = false,
  })  : id = DateTime.now().microsecondsSinceEpoch.toString(),
        createdAt = DateTime.now();

  Note.withId({
    required this.id,
    required this.title,
    required this.content,
    required this.createdAt,
    required this.tags,
    required this.isEncrypted,
  });

  bool hasTag(String tag) => tags.contains(tag);
}

enum TimeFilter { all, today, thisWeek }

// ==================== 编辑页面（增强加密）====================
class NoteEditorPage extends StatefulWidget {
  final Note? existingNote;
  final bool isEditingEncrypted; // 是否正在编辑已解密的加密笔记
  const NoteEditorPage({this.existingNote, this.isEditingEncrypted = false, super.key});

  @override
  State<NoteEditorPage> createState() => _NoteEditorPageState();
}

class _NoteEditorPageState extends State<NoteEditorPage> {
  late final TextEditingController _titleController;
  late final TextEditingController _contentController;
  late final TextEditingController _tagsController;
  bool _isEncrypted = false;

  @override
  void initState() {
    super.initState();
    if (widget.existingNote != null) {
      _titleController = TextEditingController(text: widget.existingNote!.title);
      _contentController = TextEditingController(text: widget.existingNote!.content);
      _tagsController = TextEditingController(text: widget.existingNote!.tags.join(', '));
      _isEncrypted = widget.existingNote!.isEncrypted;
    } else {
      _titleController = TextEditingController();
      _contentController = TextEditingController();
      _tagsController = TextEditingController();
      _isEncrypted = false;
    }
  }

  @override
  void dispose() {
    _titleController.dispose();
    _contentController.dispose();
    _tagsController.dispose();
    super.dispose();
  }

  List<String> _parseTags(String input) {
    return input
        .split(',')
        .map((e) => e.trim())
        .where((e) => e.isNotEmpty)
        .toSet()
        .toList();
  }

  Future<String?> _showSetPasswordDialog() async {
    final controller1 = TextEditingController();
    final controller2 = TextEditingController();
    bool passwordsMatch = false;

    return await showDialog<String>(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: const Text('设置笔记密码'),
          content: StatefulBuilder(
            builder: (context, setState) {
              return Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  TextField(
                    controller: controller1,
                    decoration: const InputDecoration(hintText: '输入6位数字密码'),
                    keyboardType: TextInputType.number,
                    maxLength: 6,
                    obscureText: true,
                  ),
                  const SizedBox(height: 8),
                  TextField(
                    controller: controller2,
                    decoration: InputDecoration(
                      hintText: '再次输入',
                      errorText: passwordsMatch ? null : '两次密码不一致',
                    ),
                    keyboardType: TextInputType.number,
                    maxLength: 6,
                    obscureText: true,
                    onChanged: (_) {
                      setState(() {
                        passwordsMatch = controller1.text == controller2.text &&
                                        controller1.text.length == 6;
                      });
                    },
                  ),
                  const SizedBox(height: 16),
                  Text(
                    '⚠️ 忘记密码将无法恢复笔记内容！',
                    style: TextStyle(color: Theme.of(context).colorScheme.error),
                  ),
                ],
              );
            },
          ),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context),
              child: const Text('取消'),
            ),
            ElevatedButton(
              onPressed: passwordsMatch
                  ? () {
                      Navigator.pop(context, controller1.text);
                    }
                  : null,
              child: const Text('确定'),
            ),
          ],
        );
      },
    );
  }

  Future<void> _saveNote() async {
    final title = _titleController.text.trim();
    if (title.isEmpty) return;
    final tags = _parseTags(_tagsController.text);
    
    // 处理加密逻辑
    String finalContent = _contentController.text.trim();
    bool shouldEncrypt = _isEncrypted;
    
    if (shouldEncrypt && (widget.existingNote?.isEncrypted == false || widget.existingNote == null)) {
      // 首次加密
      final password = await _showSetPasswordDialog();
      if (password == null) {
        // 用户取消，不保存
        return;
      }
      try {
        finalContent = await encryptContent(finalContent, password);
      } catch (e) {
        if (!mounted) return;
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(content: Text('加密失败: $e')),
        );
        return;
      }
    }

    final note = Note.withId(
      id: widget.existingNote?.id ?? DateTime.now().microsecondsSinceEpoch.toString(),
      title: title,
      content: finalContent,
      createdAt: widget.existingNote?.createdAt ?? DateTime.now(),
      tags: tags,
      isEncrypted: shouldEncrypt,
    );

    if (!mounted) return;
    Navigator.pop(context, note);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.existingNote == null ? '新建笔记' : '编辑笔记'),
        actions: [IconButton(icon: const Icon(Icons.save), onPressed: _saveNote)],
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: SingleChildScrollView(
          child: Column(
            children: [
              TextField(
                controller: _titleController,
                decoration: InputDecoration(
                  hintText: '标题',
                  border: InputBorder.none,
                  focusedBorder: InputBorder.none,
                ),
                style: const TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
                maxLines: 1,
              ),
              const Divider(height: 24),
              TextField(
                controller: _contentController,
                decoration: InputDecoration(
                  hintText: '写下你的想法...',
                  border: InputBorder.none,
                  focusedBorder: InputBorder.none,
                ),
                maxLines: null,
                keyboardType: TextInputType.multiline,
              ),
              const SizedBox(height: 16),
              TextField(
                controller: _tagsController,
                decoration: InputDecoration(
                  hintText: '标签（用逗号分隔，如：工作, 会议）',
                  border: OutlineInputBorder(),
                  focusedBorder: OutlineInputBorder(),
                ),
                maxLines: 1,
              ),
              const SizedBox(height: 16),
              ListTile(
                title: const Text('加密此笔记'),
                subtitle: const Text('开启后需设置6位数字密码，忘记密码将无法恢复内容'),
                trailing: Switch(
                  value: _isEncrypted,
                  onChanged: (value) {
                    setState(() {
                      _isEncrypted = value;
                    });
                  },
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

// ==================== 主界面（增强解密）====================
class HomePage extends StatefulWidget {
  const HomePage({super.key});

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final List<Note> _allNotes = [];
  List<Note> _filteredNotes = [];
  String _searchQuery = '';
  String? _selectedTag;
  TimeFilter _timeFilter = TimeFilter.all;
  Set<String> _allTags = {};
  late FocusNode _searchFocusNode;
  Timer? _debounceTimer;

  @override
  void initState() {
    super.initState();
    _searchFocusNode = FocusNode();
    _filteredNotes = _allNotes;
  }

  @override
  void dispose() {
    _debounceTimer?.cancel();
    _searchFocusNode.dispose();
    super.dispose();
  }

  void _updateAllTags() {
    final tags = <String>{};
    for (final note in _allNotes) {
      tags.addAll(note.tags);
    }
    setState(() {
      _allTags = tags;
    });
  }

  void _applyFilters() {
    List<Note> result = _allNotes;
    result = _filterByTime(result, _timeFilter);
    if (_selectedTag != null) {
      result = result.where((note) => note.hasTag(_selectedTag!)).toList();
    }
    if (_searchQuery.isNotEmpty) {
      final lowerQuery = _searchQuery.toLowerCase();
      result = result.where((note) {
        return note.title.toLowerCase().contains(lowerQuery) ||
               note.tags.any((tag) => tag.toLowerCase().contains(lowerQuery));
        // 注意：加密笔记的 content 不参与搜索！
      }).toList();
    }
    setState(() {
      _filteredNotes = result;
    });
  }

  List<Note> _filterByTime(List<Note> notes, TimeFilter filter) {
    if (filter == TimeFilter.all) return notes;
    final now = DateTime.now();
    return notes.where((note) {
      if (filter == TimeFilter.today) {
        return note.createdAt.year == now.year &&
               note.createdAt.month == now.month &&
               note.createdAt.day == now.day;
      } else if (filter == TimeFilter.thisWeek) {
        final weekStart = now.subtract(Duration(days: now.weekday - 1));
        final weekEnd = weekStart.add(const Duration(days: 7));
        return note.createdAt.isAfter(weekStart) && note.createdAt.isBefore(weekEnd);
      }
      return true;
    }).toList();
  }

  void _enterSearchMode() {
    setState(() {
      _isSearching = true;
      _searchQuery = '';
    });
    _searchFocusNode.requestFocus();
    _applyFilters();
  }

  void _exitSearchMode() {
    setState(() {
      _isSearching = false;
      _searchQuery = '';
    });
    _searchFocusNode.unfocus();
    _applyFilters();
  }

  void _onSearchQueryChanged(String query) {
    _debounceTimer?.cancel();
    _debounceTimer = Timer(const Duration(milliseconds: 300), () {
      setState(() {
        _searchQuery = query.trim();
      });
      _applyFilters();
    });
  }

  Future<String?> _showPasswordInputDialog(String title) async {
    final controller = TextEditingController();
    return await showDialog<String>(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: Text('输入密码 - $title'),
          content: TextField(
            controller: controller,
            decoration: const InputDecoration(hintText: '6位数字密码'),
            keyboardType: TextInputType.number,
            maxLength: 6,
            obscureText: true,
          ),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context),
              child: const Text('取消'),
            ),
            ElevatedButton(
              onPressed: () {
                if (controller.text.length == 6) {
                  Navigator.pop(context, controller.text);
                }
              },
              child: const Text('确定'),
            ),
          ],
        );
      },
    );
  }

  void _onAddNote() {
    Navigator.push(context, MaterialPageRoute(builder: (_) => const NoteEditorPage()))
        .then((result) {
      if (result != null && result is Note) {
        setState(() {
          _allNotes.insert(0, result);
        });
        _updateAllTags();
        _applyFilters();
      }
    });
  }

  void _onEditNote(Note note) async {
    if (note.isEncrypted) {
      final password = await _showPasswordInputDialog(note.title);
      if (password == null) return;
      
      try {
        final decryptedContent = await decryptContent(note.content, password);
        if (!mounted) return;
        final tempNote = Note.withId(
          id: note.id,
          title: note.title,
          content: decryptedContent,
          createdAt: note.createdAt,
          tags: note.tags,
          isEncrypted: true,
        );
        _navigateToEditor(tempNote);
      } catch (e) {
        if (!mounted) return;
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(content: const Text('密码错误，请重试')),
        );
      }
    } else {
      _navigateToEditor(note);
    }
  }

  void _navigateToEditor(Note note) {
    Navigator.push(
      context,
      MaterialPageRoute(
        builder: (_) => NoteEditorPage(
          existingNote: note,
          isEditingEncrypted: note.isEncrypted,
        ),
      ),
    ).then((result) {
      if (result != null && result is Note) {
        setState(() {
          final index = _allNotes.indexWhere((n) => n.id == result.id);
          if (index != -1) {
            _allNotes[index] = result;
          } else {
            _allNotes.insert(0, result);
          }
        });
        _updateAllTags();
        _applyFilters();
      }
    });
  }

  void _onDeleteNote(Note note) {
    setState(() {
      _allNotes.removeWhere((n) => n.id == note.id);
    });
    _updateAllTags();
    _applyFilters();
    ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('已删除 "${note.title}"')));
  }

  String _formatTime(DateTime time) {
    return '${time.year}-${time.month.toString().padLeft(2, '0')}-${time.day.toString().padLeft(2, '0')} '
        '${time.hour.toString().padLeft(2, '0')}:${time.minute.toString().padLeft(2, '0')}';
  }

  Widget _buildNoteCard(Note note) {
    return Card(
      margin: const EdgeInsets.only(bottom: 12),
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Row(
              children: [
                Expanded(
                  child: Text(
                    note.title,
                    style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
                    maxLines: 1,
                    overflow: TextOverflow.ellipsis,
                  ),
                ),
                if (note.isEncrypted)
                  Icon(Icons.lock_outline, size: 16, color: Theme.of(context).hintColor),
              ],
            ),
            const SizedBox(height: 8),
            if (note.content.isNotEmpty && !note.isEncrypted)
              Text(note.content, maxLines: 2, overflow: TextOverflow.ellipsis),
            const SizedBox(height: 8),
            if (note.tags.isNotEmpty)
              Wrap(
                spacing: 6,
                runSpacing: 4,
                children: note.tags.map((tag) {
                  return Chip(label: Text('#$tag'));
                }).toList(),
              ),
            const SizedBox(height: 8),
            Text(_formatTime(note.createdAt), style: const TextStyle(fontSize: 12)),
          ],
        ),
      ),
    );
  }

  Widget _buildNoteItem(Note note, int index) {
    return Dismissible(
      key: ValueKey(note.id),
      direction: DismissDirection.endToStart,
      background: Container(
        color: Theme.of(context).colorScheme.error,
        alignment: Alignment.centerRight,
        padding: const EdgeInsets.only(right: 20),
        child: const Icon(Icons.delete, color: Colors.white),
      ),
      onDismissed: (direction) => _onDeleteNote(note),
      child: GestureDetector(
        onTap: () => _onEditNote(note),
        child: _buildNoteCard(note),
      ),
    );
  }

  // ... 其余 UI 构建方法（_buildSearchField, _buildTagFilterBar 等）同第四篇 ...

  bool _isSearching = false;

  Widget _buildSearchField() {
    if (!_isSearching) {
      return const Text('我的笔记', style: TextStyle(fontWeight: FontWeight.w500));
    }
    return TextField(
      focusNode: _searchFocusNode,
      onChanged: _onSearchQueryChanged,
      decoration: InputDecoration(
        hintText: '搜索标题或标签...',
        hintStyle: TextStyle(color: Theme.of(context).hintColor),
        border: InputBorder.none,
        focusedBorder: InputBorder.none,
        prefixIcon: Icon(Icons.search, color: Theme.of(context).hintColor),
        suffixIcon: _searchQuery.isNotEmpty
            ? IconButton(
                icon: const Icon(Icons.clear, size: 18),
                onPressed: () {
                  _onSearchQueryChanged('');
                  WidgetsBinding.instance.addPostFrameCallback((_) {
                    if (_searchFocusNode.hasFocus) {
                      _searchFocusNode.requestFocus();
                    }
                  });
                },
              )
            : null,
      ),
      style: const TextStyle(fontSize: 16),
    );
  }

  Widget _buildTagFilterBar() {
    if (_allTags.isEmpty) return const SizedBox.shrink();
    return SingleChildScrollView(
      scrollDirection: Axis.horizontal,
      padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
      child: Row(
        children: [
          _buildFilterChip('全部', null, _selectedTag == null),
          ..._allTags.map((tag) {
            return _buildFilterChip(tag, tag, _selectedTag == tag);
          }),
        ],
      ),
    );
  }

  Widget _buildFilterChip(String label, String? value, bool isSelected) {
    return FilterChip(
      label: Text(label),
      selected: isSelected,
      onSelected: (selected) {
        setState(() {
          _selectedTag = selected ? value : null;
          _applyFilters();
        });
      },
    );
  }

  Widget _buildTimeFilter() {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
      child: SegmentedButton<TimeFilter>(
        segments: const [
          ButtonSegment<TimeFilter>(value: TimeFilter.all, label: Text('全部')),
          ButtonSegment<TimeFilter>(value: TimeFilter.today, label: Text('今日')),
          ButtonSegment<TimeFilter>(value: TimeFilter.thisWeek, label: Text('本周')),
        ],
        selected: {_timeFilter},
        onSelectionChanged: (Set<TimeFilter> newSelection) {
          setState(() {
            _timeFilter = newSelection.first;
            _applyFilters();
          });
        },
      ),
    );
  }

  Widget _buildNoteList() {
    if (_filteredNotes.isEmpty) {
      if (_searchQuery.isNotEmpty || _selectedTag != null) {
        return Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Icon(Icons.search_off, size: 64, color: Theme.of(context).hintColor),
              const SizedBox(height: 16),
              const Text('未找到匹配的笔记'),
            ],
          ),
        );
      } else {
        return const Center(child: Text('暂无笔记'));
      }
    }
    return ListView.builder(
      padding: const EdgeInsets.only(top: 8),
      itemCount: _filteredNotes.length,
      itemBuilder: (context, index) => _buildNoteItem(_filteredNotes[index], index),
    );
  }

  Widget _buildDrawer(BuildContext context) {
    return Drawer(
      child: ListView(
        padding: EdgeInsets.zero,
        children: [
          DrawerHeader(
            decoration: BoxDecoration(color: Theme.of(context).colorScheme.primary),
            child: const Text('设置', style: TextStyle(color: Colors.white, fontSize: 24)),
          ),
          ListTile(
            title: const Text('主题'),
            trailing: ValueListenableBuilder<ThemeMode>(
              valueListenable: ThemeManager.themeMode,
              builder: (context, mode, child) {
                return DropdownButton<ThemeMode>(
                  value: mode,
                  items: const [
                    DropdownMenuItem(value: ThemeMode.system, child: Text('跟随系统')),
                    DropdownMenuItem(value: ThemeMode.light, child: Text('日间模式')),
                    DropdownMenuItem(value: ThemeMode.dark, child: Text('夜间模式')),
                  ],
                  onChanged: (value) {
                    if (value != null) {
                      ThemeManager.themeMode.value = value;
                    }
                  },
                  underline: Container(),
                );
              },
            ),
          ),
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: _buildSearchField(),
        leading: _isSearching
            ? IconButton(icon: const Icon(Icons.arrow_back), onPressed: _exitSearchMode)
            : null,
        actions: !_isSearching
            ? [IconButton(icon: const Icon(Icons.search), onPressed: _enterSearchMode)]
            : null,
      ),
      drawer: !_isSearching ? _buildDrawer(context) : null,
      body: Column(
        children: [
          if (!_isSearching) ...[
            _buildTimeFilter(),
            _buildTagFilterBar(),
          ],
          Expanded(child: _buildNoteList()),
        ],
      ),
      floatingActionButton: !_isSearching
          ? FloatingActionButton(onPressed: _onAddNote, child: const Icon(Icons.add))
          : null,
    );
  }
}

// ==================== 主程序入口（同第四篇）====================
class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangePlatformBrightness() {
    if (ThemeManager.themeMode.value == ThemeMode.system) {
      setState(() {});
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: lightTheme,
      darkTheme: darkTheme,
      themeMode: ThemeManager.themeMode.value == ThemeMode.system
          ? ThemeMode.system
          : ThemeManager.themeMode.value,
      home: HomePage(),
    );
  }
}

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

运行界面

💡 注意：
以上代码中的加密为 简化实现（固定 IV + 密码填充）。在真实产品中，应使用 PBKDF2 密钥派生 + 随机盐值，并考虑集成 flutter_secure_storage 以增强安全性。

---

结语

本文成功为鸿蒙记事本添加了 单笔记加密功能，通过 AES-256 本地加密 与 清晰的用户交互，在便捷性与安全性之间取得平衡。用户现在可以放心记录敏感信息，即使设备丢失，隐私依然受保护。

至此，我们的记事本已具备 专业级功能矩阵：

• ✍️ 基础 CRUD
• 🔍 全局搜索
• 🏷️ 标签与时间分类
• 🌙 智能夜间模式
• 🔒 单笔记加密