错误：“AppStateNotifier”类型的值不能分配给“Widget”类型的变量

Posted 2023-02-23

【中文标题】错误：“AppStateNotifier”类型的值不能分配给“Widget”类型的变量

【英文标题】：Error: A value of type 'AppStateNotifier' can't be assigned to a variable of type 'Widget

【发布时间】：2020-11-25 00:05:00

【问题描述】：

按照本教程。 https://itnext.io/app-theming-in-flutter-dark-mode-light-mode-27d9adf3cee

void main() 
  WidgetsFlutterBinding.ensureInitialized();
  SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp,
    DeviceOrientation.portraitDown,
  ]);
  runApp(
    ChangeNotifierProvider<AppStateNotifier>(
      builder: (context) => AppStateNotifier(), //<--COMPILER ERROR, details below.
      child: MyApp(),
    ),
  );


class MyApp extends StatelessWidget 
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) 
    return Consumer<AppStateNotifier>(
      builder: (context, appState, child) 
        return MaterialApp(
          title: 'Lockify',
          debugShowCheckedModeBanner: false,
          theme: AppTheme.lightTheme, 
          darkTheme:
              AppTheme.darkTheme, 
          home: MyHomePage(),
          themeMode: appState.isDarkModeOn ? ThemeMode.dark : ThemeMode.light,
        );
      ,
    );
  

错误： 编译器消息： lib/main.dart:16:29：。

“AppStateNotifier”来自“package:lockify/appstatenotifier.dart”（“lib/appstatenotifier.dart”）。 'Widget' 来自'package:flutter/src/widgets/framework.dart' ('../../Developer/flutter/packages/flutter/lib/src/widgets/framework.dart')。 builder: (context) => AppStateNotifier(),

lib/main.dart:16:16: 错误：无法将参数类型“Widget Function(BuildContext)”分配给参数类型“Widget Function(BuildContext, Widget)”。

'Widget' 来自'package:flutter/src/widgets/framework.dart' ('../../Developer/flutter/packages/flutter/lib/src/widgets/framework.dart')。 “BuildContext”来自“package:flutter/src/widgets/framework.dart”（“../../Developer/flutter/packages/flutter/lib/src/widgets/framework.dart”）。 builder: (context) => AppStateNotifier(),

【参考方案1】：

尝试在ChangeNotifierProvider 小部件上将builder 更改为create。