将我的集团应用程序迁移到空安全。错误："赋值块"不符合类型参数的绑定'BlocBase<AssignmentState>' 'B'

Question

我正在将我的flutter应用程序迁移到零安全，我在BlocProvider和BlocBuilder上收到了这个错误。

'AssignmentBloc' doesn't conform to the bound 'BlocBase<AssignmentState>' of the type parameter 'B'.
Try using a type that is or is a subclass of 'BlocBase<AssignmentState>'.

我已经检查了类似问题的解决方案，在我看来，我已经按照他们的建议做了。不过，我可能错过了什么，我需要帮助。

小部件。

class _AssignmentScreenWidgetState extends State<_AssignmentScreenWidget> {
AssignmentBloc? _bloc;
bool assignmentAdd = false;
@override
void initState() {
super.initState();
_bloc = BlocProvider.of<AssignmentBloc>(context)
..add(FetchEvent(widget.courseId, widget.assignmentId));
}
final GlobalKey<AssignmentDraftWidgetState> assignmentDraftWidgetState =
GlobalKey<AssignmentDraftWidgetState>();
@override
Widget build(BuildContext context) {
return BlocListener<AssignmentBloc, AssignmentState>( // where the errors are
bloc: _bloc,
listener: (BuildContext context, AssignmentState state) {
if (state is CacheWarningAssignmentState) {
showDialog(
context: context, builder: (context) => WarningLessonDialog());
}
},
child: BlocBuilder<AssignmentBloc, AssignmentState>( // where the errors are
builder: (context, state) {
return Scaffold(
...

集团。

class AssignmentBloc extends Bloc<AssignmentEvent, AssignmentState?> {
final AssignmentRepository _assignmentRepository;
final CacheManager cacheManager;
AssignmentBloc(this._assignmentRepository, this.cacheManager) : super(null);
@override
AssignmentState get initialState => InitialAssignmentState();
...

州。

@immutable
abstract class AssignmentState {}
class InitialAssignmentState extends AssignmentState {}
class LoadedAssignmentState extends AssignmentState {
final AssignmentResponse assignmentResponse;
LoadedAssignmentState(this.assignmentResponse);
}
class ErrorAssignmentState extends AssignmentState {}
class CacheWarningAssignmentState extends AssignmentState {}

求你了，我能得到的所有帮助都非常感激。

Answer 1

您的_bloc变量实际上不可为null。它只是在构造函数中不可用。

因此，将其设为late，而不是可为null：

late AssignmentBloc _bloc;

这应该可以解决您以后的问题，因为现在您的块的类型参数不再是AssignmentBloc?，而是真正的AssignmentBloc。