解决 You should only use GetX or Obx for the specific widget that will be updated

The following message was thrown building Obx(dirty, state: _ObxState#777c8):
      [Get] the improper use of a GetX has been detected. 
      You should only use GetX or Obx for the specific widget that will be updated.
      If you are seeing this error, you probably did not insert any observable variables into GetX/Obx 
      or insert them outside the scope that GetX considers suitable for an update 
      (example: GetX => HeavyWidget => variableObservable).
      If you need to update a parent widget and a child widget, wrap each one in an Obx/GetX.

Obx或GetX组件错误使用，因为检测到在其中没有使用observable变量

Obx类型

class Obx extends ObxWidget {
  final WidgetCallback builder;

  const Obx(this.builder);

  @override
  Widget build() => builder();
}

Obx的定义很简单，它仅接受一个返回Widget的闭包作为参数

Obx 继承自 ObxWidget , ObxWidget 里面包含了本次的报错内容

  Widget get notifyChilds {
    final observer = RxInterface.proxy; // 2
    RxInterface.proxy = _observer; // 3
    final result = widget.build();
    // 1
    if (!_observer!.canUpdate) {
      throw """
      [Get] the improper use of a GetX has been detected. 
      You should only use GetX or Obx for the specific widget that will be updated.
      If you are seeing this error, you probably did not insert any observable variables into GetX/Obx 
      or insert them outside the scope that GetX considers suitable for an update 
      (example: GetX => HeavyWidget => variableObservable).
      If you need to update a parent widget and a child widget, wrap each one in an Obx/GetX.
      """;
    }
    RxInterface.proxy = observer; // 4
    return result;
  }

_observer!.canUpdate为false才抛出的错误

查看 _observer 为 RxNotifier实例

class _ObxState extends State<ObxWidget> {
  final _observer = RxNotifier();
  late StreamSubscription subs;

  @override
  void initState() {
    super.initState();
    subs = _observer.listen(_updateTree, cancelOnError: false);
  }

  void _updateTree(_) {
    if (mounted) {
      setState(() {});
    }
  }

  @override
  void dispose() {
    subs.cancel();
    _observer.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) =>
      RxInterface.notifyChildren(_observer, widget.build);
}

RxNotifier的实现

class RxNotifier<T> = RxInterface<T> with NotifyManager<T>;

mixin NotifyManager<T> {
  GetStream<T> subject = GetStream<T>();
  final _subscriptions = <GetStream, List<StreamSubscription>>{};

  bool get canUpdate => _subscriptions.isNotEmpty;

  /// This is an internal method.
  /// Subscribe to changes on the inner stream.
  void addListener(GetStream<T> rxGetx) {
    if (!_subscriptions.containsKey(rxGetx)) {
      final subs = rxGetx.listen((data) {
        if (!subject.isClosed) subject.add(data);
      });
      final listSubscriptions =
          _subscriptions[rxGetx] ??= <StreamSubscription>[];
      listSubscriptions.add(subs);
    }
  }

  StreamSubscription<T> listen(
    void Function(T) onData, {
    Function? onError,
    void Function()? onDone,
    bool? cancelOnError,
  }) =>
      subject.listen(
        onData,
        onError: onError,
        onDone: onDone,
        cancelOnError: cancelOnError ?? false,
      );

  /// Closes the subscriptions for this Rx, releasing the resources.
  void close() {
    _subscriptions.forEach((getStream, _subscriptions) {
      for (final subscription in _subscriptions) {
        subscription.cancel();
      }
    });

    _subscriptions.clear();
    subject.close();
  }
}

canUpdate 时 _subscriptions.isNotEmpty 不能为空

mixin RxObjectMixin<T> on NotifyManager<T> {
  // ...
  T get value {
    if (RxInterface.proxy != null) {
      RxInterface.proxy!.addListener(subject);
    }
    return _value;
  }
  // ...
}

使用了.value方法，使用proxy记录下使用记录，并listen这个变量, 在访问value时，Obx尚未创建，也没有对应的RxNotifier可供记录和监听用