延迟初始化错误：本地"首选项"尚未初始化

Question

我正在使用riverpod和flutter_hooks

我正在尝试使用这两种方法来实现shared_prefrences，这就是我目前所做的：

pref_changenotifier.dart

import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
const _isloggedkey = 'logged';
const _boardingkey = "boarding";
const _apiTokenkey = 'apitoken';
const _rolekey = 'role';
class PrefChangeNotifier with ChangeNotifier {
late final SharedPreferences _sharedPreferences;
PrefChangeNotifier(this._sharedPreferences) {
getPref();
notifyListeners();
}
bool? _islogged;
bool? _boarding;
String? _apitoken;
String? _role;
String get apitoken => _apitoken!;
String get role => _role!;
bool get islogged => _islogged!;
bool get boarding => _boarding!;
void getPref() async {
_islogged = _sharedPreferences.getBool(_isloggedkey);
_apitoken = _sharedPreferences.getString(_apiTokenkey);
_boarding = _sharedPreferences.getBool(_boardingkey);
notifyListeners();
}
void setLoggedValue(bool logged) async {
await _sharedPreferences.setBool(_isloggedkey, logged);
_islogged = logged;
notifyListeners();
}
void setTokenValue(String apitoken) async {
await _sharedPreferences.setString(_apiTokenkey, apitoken);
_apitoken = apitoken;
notifyListeners();
}
void setBoardingValue(bool boarding) async {
await _sharedPreferences.setBool(_boardingkey, boarding);
_boarding = boarding;
notifyListeners();
}
void setRoleValue(String role) async {
await _sharedPreferences.setString(_rolekey, role);
_role = role;
notifyListeners();
}
void clearAllValues() async {
await _sharedPreferences.clear();
notifyListeners();
}
}

pref_provider.dart

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'pref_changenotifier.dart';
import 'package:shared_preferences/shared_preferences.dart';
final sharedPreferences = FutureProvider<SharedPreferences>(
(ref) async => await SharedPreferences.getInstance());
final prefChangeNotifierProvider =
ChangeNotifierProvider<PrefChangeNotifier>((ref) {
final sharePreferencesData = ref.watch(sharedPreferences).asData;
late final SharedPreferences prefs;
if (sharePreferencesData != null) {
prefs = sharePreferencesData.value;
}
return PrefChangeNotifier(prefs);
});

但每当我用ref.read(prefChangeNotifierProvider).setBoardingValue(true);调用它时，它就会抛出这个错误

E/flutter (22947): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: An exception was thrown while building ChangeNotifierProvider<PrefChangeNotifier>#05878.
E/flutter (22947):
E/flutter (22947): Thrown exception:
E/flutter (22947): An exception was thrown while building _NotifierProvider<PrefChangeNotifier>#3bb8a.
E/flutter (22947):
E/flutter (22947): Thrown exception:
E/flutter (22947): LateInitializationError: Local 'prefs' has not been initialized.
E/flutter (22947):
E/flutter (22947): Stack trace:

我知道问题出在初始化延迟，但我该怎么办？

Answer 1

是的，这不是很明显吗？您使用late final SharedPreferences prefs，然后使用prefs = sharePreferencesData.value。您尚未启动该变量，因此无法对其执行任何操作。您可以在async函数中将其更改为：final SharedPreferences prefs = await SharedPreferences.getInstance()。

关于代码的另一个问题是，当您调用getBool((、getString((，它可能为null(如果您没有在共享偏好中保存任何内容(。你可以使用这样的东西：

isLogin = prefs.getBool(SHARED_PREFS_KEY_LOGIN) ?? false;

Answer 2

将此方法放入PrefChangeNotifier类

static Future initMySharedPreferences() async {
_sharedPreferences = await SharedPreferences.getInstance();
}

并在main.dart 中初始化

void main() async {
WidgetsFlutterBinding.ensureInitialized();
await PrefChangeNotifier.initMySharedPreferences();
runApp(MyApp());
}