试图从小部件树外部监听提供者公开的值

Question

所以，我有一个 flutter 项目，我正在尝试构建一个卡片列表，其中的内容取决于我的 OrderModel 类，我正在尝试使用 Provider 来实现这一点，但我收到了这个错误：

????????? 调度程序库捕获的异常??????????????????????????????

试图从小部件树外部监听提供者公开的值。

这可能是由调用 Provider.of 而不传递 的事件处理程序（如按钮的 onPressed）引起的listen: false。

要修复，请编写：Provider.of(context, listen: false);

它不受支持，因为当小部件树不关心该值时，可能会毫无意义地重建与事件处理程序关联的小部件。'package:provider/src/provider.dart'：断言失败：第 193 行位置 7：'context.owner.debugBuilding || 听 == 假 || _debugIsInInheritedProviderUpdate'

抛出异常时，这是堆栈

#2 Provider.of 包：provider/src/provider.dart:193

#3 _OrderHistoryState._onAfterBuild 包：shinier_store/screens/order_history.dart:60

#4 _OrderHistoryState.build。包：shinier_store/screens/order_history.dart:67

#5 SchedulerBinding._invokeFrameCallback package:flutter/…/scheduler/binding.dart:1102

#6 SchedulerBinding.handleDrawFrame 包：flutter/.../scheduler/binding.dart:1049 ...

?????????????????????????????????????????????????????? ??????? _onAfterBuild() 中提供程序调用的堆栈跟踪

I/flutter ( 3092): #0      _AssertionError._doThrowNew  (dart:core-patch/errors_patch.dart:42:39)
I/flutter ( 3092): #1      _AssertionError._throwNew  (dart:core-patch/errors_patch.dart:38:5)
I/flutter ( 3092): #2      Provider.of package:provider/src/provider.dart:193
I/flutter ( 3092): #3      _OrderHistoryState._onAfterBuild package:shinier_store/screens/order_history.dart:61
I/flutter ( 3092): #4      _OrderHistoryState.build.<anonymous closure> 
package:shinier_store/screens/order_history.dart:71
I/flutter ( 3092): #5      SchedulerBinding._invokeFrameCallback 
package:flutter/…/scheduler/binding.dart:1102
I/flutter ( 3092): #6      SchedulerBinding.handleDrawFrame 
package:flutter/…/scheduler/binding.dart:1049
I/flutter ( 3092): #7      SchedulerBinding._handleDrawFrame 
package:flutter/…/scheduler/binding.dart:957
I/flutter ( 3092): #8      _rootRun  (dart:async/zone.dart:1126:13)
I/flutter ( 3092): #9      _CustomZone.run  (dart:async/zone.dart:1023:19)
I/flutter ( 3092): #10     _CustomZone.runGuarded  (dart:async/zone.dart:925:7)
I/flutter ( 3092): #11     _invoke  (dart:ui/hooks.dart:259:10)
I/flutter ( 3092): #12     _drawFrame  (dart:ui/hooks.dart:217:3)

我不知道我怎么可能解决它，因为我在我的 Provider 调用中添加了 listen:false 。我尝试使用 WidgetBinding，因为我认为 Provider 调用应该在构建完成后进行，但这似乎并没有解决问题。

以下是代码：

订单模型类

I/flutter ( 3092): #0      _AssertionError._doThrowNew  (dart:core-patch/errors_patch.dart:42:39)
I/flutter ( 3092): #1      _AssertionError._throwNew  (dart:core-patch/errors_patch.dart:38:5)
I/flutter ( 3092): #2      Provider.of package:provider/src/provider.dart:193
I/flutter ( 3092): #3      _OrderHistoryState._onAfterBuild package:shinier_store/screens/order_history.dart:61
I/flutter ( 3092): #4      _OrderHistoryState.build.<anonymous closure> 
package:shinier_store/screens/order_history.dart:71
I/flutter ( 3092): #5      SchedulerBinding._invokeFrameCallback 
package:flutter/…/scheduler/binding.dart:1102
I/flutter ( 3092): #6      SchedulerBinding.handleDrawFrame 
package:flutter/…/scheduler/binding.dart:1049
I/flutter ( 3092): #7      SchedulerBinding._handleDrawFrame 
package:flutter/…/scheduler/binding.dart:957
I/flutter ( 3092): #8      _rootRun  (dart:async/zone.dart:1126:13)
I/flutter ( 3092): #9      _CustomZone.run  (dart:async/zone.dart:1023:19)
I/flutter ( 3092): #10     _CustomZone.runGuarded  (dart:async/zone.dart:925:7)
I/flutter ( 3092): #11     _invoke  (dart:ui/hooks.dart:259:10)
I/flutter ( 3092): #12     _drawFrame  (dart:ui/hooks.dart:217:3)

order_history.dart - 状态类

class OrderModel extends ChangeNotifier {
  List<Order> myOrders;
  bool isLoading = true;
  String errMsg;
  int page = 1;
  bool endPage = false;

  void getMyOrder({UserModel userModel}) async {
    try {
      isLoading = true;
      notifyListeners();
      myOrders = await WooCommerce().getMyOrders(userModel: userModel, page: 1);
      page = 1;
      errMsg = null;
      isLoading = false;
      endPage = false;
      notifyListeners();
    } catch (err) {
      errMsg =
          "There is an issue with the app during request the data, please contact admin for fixing the issues " +
              err.toString();
      isLoading = false;
      notifyListeners();
    }
  }

  void loadMore({UserModel userModel}) async {
    try {
      isLoading = true;
      page = page + 1;
      notifyListeners();
      var orders =
          await WooCommerce().getMyOrders(userModel: userModel, page: page);
      myOrders = [...myOrders, ...orders];
      if (orders.length == 0) endPage = true;
      errMsg = null;
      isLoading = false;
      notifyListeners();
    } catch (err) {
      errMsg =
          "There is an issue with the app during request the data, please contact admin for fixing the issues " +
              err.toString();
      isLoading = false;
      notifyListeners();
    }
  }
}

main.dart - 构建方法

class _OrderHistoryState extends State<OrderHistory> {
  void _onAfterBuild(BuildContext context){
     Provider.of<OrderModel>(context, listen: false)
        .getMyOrder(userModel: Provider.of<UserModel>(context));
  }

  @override
  Widget build(BuildContext context) {
    var formatter = DateFormat('dd-MM-yyyy');
    var model = Provider.of<OrderModel>(context);
    WidgetsBinding.instance.addPostFrameCallback((_) => _onAfterBuild(context));

    return Scaffold(
      appBar: AppBar(
          title: Text(
            'Order History',
            style: TextStyle(fontWeight: FontWeight.bold),
          ),
          elevation: 0.0),
      body: model.myOrders == null ? Center() :
      Padding(
        padding: const EdgeInsets.all(10.0),
        child: ListView.separated(
          separatorBuilder: (_, __) => SizedBox(height: 10.0),
          itemCount: model.myOrders.length,
          itemBuilder: (context, index) {
            String stat = model.myOrders[index].status;
            return Card(
              color: _buildColor(stat),
              elevation: 3.5,
              ...
  }
}

Answer 1

我也遇到了类似的错误，并发现在较新版本的提供程序包（我正在使用provider: ^6.0.1）中，您必须通过listen: false更新提供程序数据的任何位置。

例如，点击按钮或任何小部件的 onChanged 事件。下面是 TextField onChanged 回调的示例。

TextField(
  onChanged: (newText) {
    Provider.of<Data>(context, listen: false).changeString(newText);
  },
);

Answer 2

如果您正在使用提供商，^6.0.2则使用：

context.read<YourFunction>()

不是：

context.watch<YourFunction>()

Answer 3

该错误似乎指出这两行代码导致了问题。

#3 _OrderHistoryState._onAfterBuild package:shinier_store/screens/order_history.dart:60

#4 _OrderHistoryState.build. package:shinier_store/screens/order_history.dart:67

您提供的重现不完整，我只能猜测所需的标志listen: false已添加到 上_onAfterBuild()。但是，错误日志指出var model = Provider.of<OrderModel>(context);内部Widget build()还需要有该标志。文档中解释了此标志要求的原因。

如果您仍然遇到问题，最小限度的重现将有助于我们理解为什么会出现这种情况。