list - 在flift中缓存两个列表

Question

我想缓存从Firebase获得的两个列表，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和意义列表供以后使用。

如果有人可以帮助，那就太好了:)

Answer 1

您的问题描述并未完全满足您的要求，但是您可以使用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()),
            ],
          ),
        ),
      ),
    );
  }
}

您无需将列表存储在 init()中，因为此示例已完成。您还可以通过多种方式将数据从一个窗口小部件传递给其他窗口小部件，如果您正在寻找状态管理，则可以使用BLOC或提供程序。