【Flutter】SharedPreferences使用

1. 引入依赖

  # https://github.com/tekartik/synchronized.dart
  synchronized: '>=3.0.0 <4.0.0'
  # https://github.com/flutter/plugins/tree/master/packages/shared_preferences
  shared_preferences: '>=2.0.3 <4.0.0'

2. SpUtil

library sp_util;

import 'dart:async';
import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';
import 'package:synchronized/synchronized.dart';

/** * @Author: Sky24n * @GitHub: https://github.com/Sky24n * @Email: [email protected] * @Date: 2018/9/8 * @Description: Sp Util. */

/// SharedPreferences Util.
class SpUtil {
    
  static SpUtil? _singleton;
  static SharedPreferences? _prefs;
  static Lock _lock = Lock();

  static Future<SpUtil?> getInstance() async {
    
    if (_singleton == null) {
    
      await _lock.synchronized(() async {
    
        if (_singleton == null) {
    
          // keep local instance till it is fully initialized.
          // 保持本地实例直到完全初始化。
          var singleton = SpUtil._();
          await singleton._init();
          _singleton = singleton;
        }
      });
    }
    return _singleton;
  }

  SpUtil._();

  Future _init() async {
    
    _prefs = await SharedPreferences.getInstance();
  }

  /// put object.
  static Future<bool>? putObject(String key, Object value) {
    
    return _prefs?.setString(key, json.encode(value));
  }

  /// get obj.
  static T? getObj<T>(String key, T f(Map v), {
    T? defValue}) {
    
    Map? map = getObject(key);
    return map == null ? defValue : f(map);
  }

  /// get object.
  static Map? getObject(String key) {
    
    String? _data = _prefs?.getString(key);
    return (_data == null || _data.isEmpty) ? null : json.decode(_data);
  }

  /// put object list.
  static Future<bool>? putObjectList(String key, List<Object> list) {
    
    List<String>? _dataList = list.map((value) {
    
      return json.encode(value);
    }).toList();
    return _prefs?.setStringList(key, _dataList);
  }

  /// get obj list.
  static List<T>? getObjList<T>(String key, T f(Map v),
      {
    List<T>? defValue = const []}) {
    
    List<Map>? dataList = getObjectList(key);
    List<T>? list = dataList?.map((value) {
    
      return f(value);
    }).toList();
    return list ?? defValue;
  }

  /// get object list.
  static List<Map>? getObjectList(String key) {
    
    List<String>? dataLis = _prefs?.getStringList(key);
    return dataLis?.map((value) {
    
      Map _dataMap = json.decode(value);
      return _dataMap;
    }).toList();
  }

  /// get string.
  static String? getString(String key, {
    String? defValue = ''}) {
    
    return _prefs?.getString(key) ?? defValue;
  }

  /// put string.
  static Future<bool>? putString(String key, String value) {
    
    return _prefs?.setString(key, value);
  }

  /// get bool.
  static bool? getBool(String key, {
    bool? defValue = false}) {
    
    return _prefs?.getBool(key) ?? defValue;
  }

  /// put bool.
  static Future<bool>? putBool(String key, bool value) {
    
    return _prefs?.setBool(key, value);
  }

  /// get int.
  static int? getInt(String key, {
    int? defValue = 0}) {
    
    return _prefs?.getInt(key) ?? defValue;
  }

  /// put int.
  static Future<bool>? putInt(String key, int value) {
    
    return _prefs?.setInt(key, value);
  }

  /// get double.
  static double? getDouble(String key, {
    double? defValue = 0.0}) {
    
    return _prefs?.getDouble(key) ?? defValue;
  }

  /// put double.
  static Future<bool>? putDouble(String key, double value) {
    
    return _prefs?.setDouble(key, value);
  }

  /// get string list.
  static List<String>? getStringList(String key,
      {
    List<String>? defValue = const []}) {
    
    return _prefs?.getStringList(key) ?? defValue;
  }

  /// put string list.
  static Future<bool>? putStringList(String key, List<String> value) {
    
    return _prefs?.setStringList(key, value);
  }

  /// get dynamic.
  static dynamic getDynamic(String key, {
    Object? defValue}) {
    
    return _prefs?.get(key) ?? defValue;
  }

  /// have key.
  static bool? haveKey(String key) {
    
    return _prefs?.getKeys().contains(key);
  }

  /// contains Key.
  static bool? containsKey(String key) {
    
    return _prefs?.containsKey(key);
  }

  /// get keys.
  static Set<String>? getKeys() {
    
    return _prefs?.getKeys();
  }

  /// remove.
  static Future<bool>? remove(String key) {
    
    return _prefs?.remove(key);
  }

  /// clear.
  static Future<bool>? clear() {
    
    return _prefs?.clear();
  }

  /// Fetches the latest values from the host platform.
  static Future<void>? reload() {
    
    return _prefs?.reload();
  }

  ///Sp is initialized.
  static bool isInitialized() {
    
    return _prefs != null;
  }

  /// get Sp.
  static SharedPreferences? getSp() {
    
    return _prefs;
  }
}

3. 初始化

void main() async {
    
  WidgetsFlutterBinding.ensureInitialized();
  await SpUtil.getInstance();
  runApp(_widgetForRoute(window.defaultRouteName));
}

初始化后就可以直接使用了。

4. 注意事项

• Flutter的sp生成的文件在data/data/包名/shared_prefs/文件夹下面
  
  如果混合开发，原生端和Flutter端调用是有些区别的，如上所示，是flutter端调用如下代码生成的FlutterSharedPreferences.xml

SpUtil.putString("result", "test");

flutter不需要我们指定文件名，而且生成后，name自动添加flutter.，上述key在sp文件中变成了flutter.result。而Flutter获取result对应的值如下所示：

String? sp = SpUtil.getString("result");

如果原生端要获取flutter创建的sp，则需要如下方式：

SharedPreferences sp = context.getSharedPreferences("FlutterSharedPreferences",
				Context.MODE_PRIVATE);
String value = sp.getString("flutter.result", "");

• 混合开发时可能报错：
  E/flutter (28814): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: MissingPluginException(No implementation found for method getAll on channel plugins.flutter.io/shared_preferences)

解决方案：在Android原生端的FlutterActivity或者FlutterFragment里面添加如下代码

    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
    
        super.configureFlutterEngine(flutterEngine);
        GeneratedPluginRegistrant.registerWith(flutterEngine);
    }