Flutter 颤振web:BlocProvider:TypeError:无法读取属性'；获取$bloc'；未定义的

我只在概要文件和发布（web）版本中遇到这个问题，但在调试版本中效果良好

所以我有一个类，它可以访问

didChangeDependencies（）

使用此设置，在调试模式下一切正常，但在配置文件构建中，我遇到以下错误：

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
js_primitives.dart:49 The following NullError was thrown building Builder:
js_primitives.dart:49 NoSuchMethodError: method not found: 'get$bloc' on null
js_primitives.dart:49 
js_primitives.dart:49 Widget creation tracking is currently disabled. Enabling it enables improved error messages. It can
js_primitives.dart:49 be enabled by passing `--track-widget-creation` to `flutter run` or `flutter test`.
js_primitives.dart:49 
js_primitives.dart:49 When the exception was thrown, this was the stack:
js_primitives.dart:49 TypeError: Cannot read property 'get$bloc' of undefined
js_primitives.dart:49     at Object.BizBlocProvider_of (https://bazon.in/app/main.dart.js:10277:126)
js_primitives.dart:49     at _CategoryPageState.didChangeDependencies$0 (https://bazon.in/app/main.dart.js:47315:25)
js_primitives.dart:49     at StatefulElement._firstBuild$0 (https://bazon.in/app/main.dart.js:85143:31)
js_primitives.dart:49     at StatefulElement.mount$2 (https://bazon.in/app/main.dart.js:85016:12)
js_primitives.dart:49     at SingleChildRenderObjectElement.inflateWidget$2 (https://bazon.in/app/main.dart.js:84733:16)
js_primitives.dart:49     at SingleChildRenderObjectElement.updateChild$3 (https://bazon.in/app/main.dart.js:84661:20)
js_primitives.dart:49     at SingleChildRenderObjectElement.mount$2 (https://bazon.in/app/main.dart.js:85506:39)
js_primitives.dart:49     at StatelessElement.inflateWidget$2 (https://bazon.in/app/main.dart.js:84733:16)
js_primitives.dart:49     at StatelessElement.updateChild$3 (https://bazon.in/app/main.dart.js:84661:20)
js_primitives.dart:49     at StatelessElement.performRebuild$0 (https://bazon.in/app/main.dart.js:85039:41)

更新1:

现在我有了一个父窗口小部件

主页

，其

didChangeDependencies（）

如下所示：

Widget build(BuildContext context) {
  return CityBlocProvider(
    child: CategoryBlocProvider(
        child: BizBlocProvider(
            child: MaterialApp( /** actual code goes here */ )
  )));
}

  @override
  void didChangeDependencies() {
    print('Home: Did Change Dependencies');
    print(context);
    print(CityBlocProvider.of(context));
    _cityBloc = CityBlocProvider.of(context);
    _categoryBloc = CategoryBlocProvider.of(context);
    super.didChangeDependencies();
  }

在本地运行上述代码时的日志为：

js_primitives.dart:32 Home: Did Change Dependencies
js_primitives.dart:32 HomePage(dirty, state: _HomePageState#eb8ac(lifecycle state: initialized))
js_primitives.dart:32 Instance of 'CityBloc'

但是当我在

profile

build中运行相同的代码时，日志是：

js_primitives.dart:49 Home: Did Change Dependencies
js_primitives.dart:49 HomePage
js_primitives.dart:49 ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
js_primitives.dart:49 The following NullError was thrown building _BodyBuilder:
js_primitives.dart:49 NoSuchMethodError: method not found: 'get$bloc' on null

主页的实例看起来不同。配置文件生成是托管的@

这里会出什么问题

js_primitives.dart:49 Home: Did Change Dependencies
js_primitives.dart:49 HomePage
js_primitives.dart:49 ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
js_primitives.dart:49 The following NullError was thrown building _BodyBuilder:
js_primitives.dart:49 NoSuchMethodError: method not found: 'get$bloc' on null