FutureBuilder快照数据类型不正确

Question

我正在使用flutter futurebuilder widget和sharedPreferences，在使用之前加载偏好以获取语言并将其传递给儿童窗口小部件。

这是我的代码：

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:i18n_extension/i18n_widget.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:shared_preferences/shared_preferences.dart';

import 'helpers/color.dart';
import 'pages/home.dart';
import '../constants.dart';

void main() {
  runApp(
    const ProviderScope(
      child: MyApp(),
    ),
  );
}

Future<SharedPreferences> getPrefs() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  return prefs;
}

Locale getLanguageSetting(SharedPreferences prefs) {
  String? lang = prefs.getString('language');
  if (LANGUAGES.contains(lang)) {
    return Locale(lang, '');
  }
  return const Locale('en', '')
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: getPrefs(),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
              return MaterialApp(
      localizationsDelegates: const [
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],
      supportedLocales: const [
        Locale('en', ''),
        Locale('jp', ''),
      ],
      home: I18n(
          initialLocale: getLanguageSetting(snapshot.data),
          child: HomeWidget(getPrefs: snapshot.data)), // to force locale to jp
    );
        } else {
          return const Center(
            child: CircularProgressIndicator(),
          );
        }
      }
    );
  }
}

但是我在snapshot.data的类型上遇到了麻烦：我将其传递给它发送的方法和小部件都将其发送回一个类型错误参数类型'对象'？无法分配到参数类型的“共享”

。 ），但似乎是类型asyncsnapshot＆lt; object？＆gt;。

为什么？我应该铸造snapshot.data sharedPreferences type（我对铸造不太满意）吗？我该怎么做？

Answer 1

将快照中的类型定义为asyncsnapshot＆lt; sharedPreferences＆gt;快照。然后，如果您正在运行NULL安全版本，则将共享Preferences的类型更改为共享流程吗？在getlanguagesetting中。

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

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

    Future<SharedPreferences> getPrefs() async {
      SharedPreferences prefs = await SharedPreferences.getInstance();
      return prefs;
    }

    class MyApp extends StatelessWidget {
      const MyApp({Key? key}) : super(key: key);

      @override
      Widget build(BuildContext context) {
        return FutureBuilder(
            future: getPrefs(),
            builder: (context, AsyncSnapshot<SharedPreferences?> snapshot) {
              if (snapshot.hasData) {
                print(snapshot.data.runtimeType);
                getLanguageSetting(snapshot.data);
                return MaterialApp(
                    localizationsDelegates: const [],
                    supportedLocales: const [
                      Locale('en', ''),
                      Locale('jp', ''),
                    ],
                    home: Container(
                      color: Colors.red,
                    ));
              } else {
                return const Center(
                  child: CircularProgressIndicator(),
                );
              }
            });
      }
    }

    void getLanguageSetting(SharedPreferences? prefs) {
      print(prefs.runtimeType);
    }