# Flutter 好用package - shared_preferences 介紹

## shared_preferences
允許你以key-value格式保存數據，這個套件的好處之一是它不需要任何設置或配置。只要創建一個套件的實例，你就可以取得和保存數據了。**但它只支持保存簡單的屬性**，如strings、numbers和boolean等。

另外，shared_preferences**並不適合儲存敏感數據**(密碼或access tokens等)，若有此需求可考慮使用flutter_secure_storage。

flutter pub add shared_preferences

[官網](https://pub.dev/packages/shared_preferences)

### 程式範例
* 儲存

void savePreviousSearches() async {
    final prefs = await SharedPreferences.getInstance();
    prefs.setStringList(prefSearchKey, previousSearches);
 }

* 讀取

//當用戶重新啟動應用程序時讀值
@override
void initState() {
    super.initState();
    getPreviousSearches();
}

void getPreviousSearches() async {
    final prefs = await SharedPreferences.getInstance();
    if (prefs.containsKey(prefSearchKey)) {
      previousSearches = prefs.getStringList(prefSearchKey) ?? <String>[];
    }
}

* 儲存int格式

void saveCurrentIndex() async {
    final prefs = await SharedPreferences.getInstance();
    prefs.setInt(prefSelectedIndexKey, _selectedIndex);
  }

* 讀取int格式

void getCurrentIndex() async {
    final prefs = await SharedPreferences.getInstance();
    if (prefs.containsKey(prefSelectedIndexKey)) {
      setState(() {
        _selectedIndex = prefs.getInt(prefSelectedIndexKey)!;
      });
    }
  }

* Bool/Double/String..依此類推

### 統整成工具包

import 'package:shared_preferences/shared_preferences.dart';

class LocalStorage {
  LocalStorage._();
  static late SharedPreferences prefs;

  static Future<void> init() async {
    prefs = await SharedPreferences.getInstance();
  }

  static Future<bool> set(String key, dynamic value) {
    if (value is String) {
      return prefs.setString(key, value);
    } else if (value is int) {
      return prefs.setInt(key, value);
    } else if (value is double) {
      return prefs.setDouble(key, value);
    } else if (value is bool) {
      return prefs.setBool(key, value);
    }
    return prefs.setStringList(key, value);
  }

  static dynamic get(String key) {
    return prefs.get(key);
  }

  static Future<bool> cleanAll() async {
    return prefs.clear();
  }

  static Future<bool> remove(String key) async {
    return prefs.remove(key);
  }

  static Future<Map<String, String>> getAllPrefs() async {
    return <String, String>{
      for (String key in prefs.getKeys()) ...{key: prefs.get(key).toString()}
    };
  }
}

###### tags: `flutter`