Flutter中get_it注入SharedPreferences报实例未就绪错误解决

开发中使用get_it做依赖注入、flutter_bloc做状态管理时，抛出如下连锁错误：

I/flutter (23661): Error while creating WeatherInfoLocalDataSource
I/flutter (23661): Error while creating WeatherInfoRepository
I/flutter (23661): Error while creating GetWeatherInfoByCityName
I/flutter (23661): Error while creating WeatherInfoBloc
════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown building _BodyBuilder:
You tried to access an instance of SharedPreferences that is not ready yet
'package:get_it/get_it_impl.dart':
package:get_it/get_it_impl.dart:1
Failed assertion: line 404 pos 9: 'instanceFactory.isReady'

The relevant error-causing widget was
Scaffold
lib\…\pages\weather_info_page.dart:25
When the exception was thrown, this was the stack
════════ Exception caught by rendering library ═════════════════════════════════
Each child must be laid out exactly once.
The relevant error-causing widget was
Scaffold

代码共存在三处问题，直接触发上述报错：

• 异步依赖未等待初始化完成：SharedPreferences通过registerSingletonAsync注册，属于异步初始化实例。原main函数调用di.init()后，没有等待所有异步实例就绪就直接启动App，导致依赖链上的本地数据源、仓储层、用例、Bloc依次初始化失败，抛出实例未就绪的断言错误；后续Scaffold构建时因为Bloc初始化异常，连带触发子组件布局次数异常的渲染错误。
• http客户端注册写法错误：注册http.Client时遗漏构造括号，实际注入容器的是Client类的构造函数引用，而非可用的Client实例，远程数据源初始化时会拿到类型不匹配的对象。
• Bloc内的异步方法调用遗漏await关键字，异步流程执行顺序不符合预期。

1. 修改main入口函数，等待依赖注册、所有异步实例初始化完成后再启动App：

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await di.init();
  // 等待所有异步注册的实例就绪
  await di.sl.allReady();
  runApp(const MyApp());
}

2. 修正依赖注入容器中http.Client的注册代码，补全构造括号：

//! External
sl.registerSingletonAsync<SharedPreferences>(
    () => SharedPreferences.getInstance());
// 补全构造括号，注册Client实例而非构造方法引用
sl.registerLazySingleton(() => http.Client());
sl.registerLazySingleton(() => InternetConnectionChecker());

3. 排查Bloc层所有异步调用逻辑，补全遗漏的await关键字，确保事件处理、用例/仓储调用按预期顺序执行。

内容的提问来源于stack exchange，提问作者Njordww