在flutter中缓存两个List

Question

我想缓存从 Firebase 获取的两个列表，以供用户离线时使用

这是我的列表显示屏幕的完整代码 -

import 'package:flutter/material.dart';

import 'package:naamaa/calculations/name-list-calc.dart';

List namesList = List();
List meaningsList = List();

class NameList extends StatefulWidget {
  @override
  _NameListState createState() => _NameListState();
}

class _NameListState extends State<NameList> {
  Future<String> getPosts() async {
    var names = await NameListCalc().nameListCalc();
    namesList.addAll(names[0]);
    meaningsList.addAll(names[1]);
    String s = 'test';
    return s;
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<String>(
      future: getPosts(),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return Scaffold(
            resizeToAvoidBottomPadding: false,
            body: ListView.builder(
              padding: EdgeInsets.zero,
              itemBuilder: (context, position) {
                return Row(
                  children: <Widget>[
                    Container(
                      width: 100,
                      child: Text(namesList[position]),
                    ),
                    Container(
                      child: Text(meaningsList[position]),
                    )
                  ],
                );
              },
              itemCount: namesList.length,
            ),
          );
        } else {
          return Text(':(');
        }
      },
    );
  }
}

我想缓存 namesList 和 meaningsList 供以后使用。

如果有人可以提供帮助，那就太好了:)

Answer 1

您的问题描述我没有得到完整的要求，但您可以使用shared_preferences 库来存储数据列表，如下所示
添加以下行 pubspec.yaml

dependencies:
  flutter:
    sdk: flutter
  shared_preferences:

您可以使用此示例并根据需要添加更多实用程序方法。

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() async {
  AppConfig.init(() {
    runApp(MyApp());
  });
}

class CustomModel {
  int id;
  String name;

  CustomModel({this.id, this.name});

  factory CustomModel.fromJson(Map<String, dynamic> json) {
    return CustomModel(id: json["id"], name: json["name"]);
  }

  Map<String, dynamic> toJson() => {"id": id, "name": name};

  @override
  String toString() {
    return "id: $id, name: $name";
  }
}

class AppConfig {
  static Future init(VoidCallback callback) async {
    WidgetsFlutterBinding.ensureInitialized();
    await SharedPreferenceUtils.init();
    callback();
  }
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class SharedPreferenceUtils {
  static SharedPreferences prefs;

  static init() async {
    prefs = await SharedPreferences.getInstance();
    // storing lists
    await putStringList("m_list", ["abc", "def"]);
    await putObjectList("data",
        [CustomModel(id: 1, name: "Bob"), CustomModel(id: 2, name: "Alice")]);
  }

  static Future<bool> putStringList(String key, List<String> list) async {
    return prefs.setStringList(key, list);
  }

  static List<String> getStringList(String key) {
    return prefs.getStringList(key);
  }

  static Future<bool> putObjectList(String key, List<Object> list) async {
    if (prefs == null) return null;
    List<String> _dataList = list?.map((value) {
      return json.encode(value);
    })?.toList();
    return prefs.setStringList(key, _dataList);
  }

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

  static List<Map> getObjectList(String key) {
    if (prefs == null) return null;
    List<String> dataList = prefs.getStringList(key);
    return dataList?.map((value) {
      Map _dataMap = json.decode(value);
      return _dataMap;
    })?.toList();
  }
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            mainAxisSize: MainAxisSize.min,
            children: <Widget>[
              Text(SharedPreferenceUtils.getStringList("m_list").toString()),
              Text(SharedPreferenceUtils.getObjList<CustomModel>(
                  "data", (v) => CustomModel.fromJson(v)).toString()),
            ],
          ),
        ),
      ),
    );
  }
}

您不需要将列表存储在init() 中，就像在本示例中所做的那样。您还可以通过多种方式将数据从一个小部件传递给其他小部件，如果您正在寻找状态管理，那么您可以使用 BLOC 或提供程序。