ProviderNotFoundException 在构建 ConsumptionDialog 时被抛出，因为使用了不包含提供者的“BuildContext”

Question

我是一名学生，我在学校没有学习移动开发。如果有人能帮助我，我真的很感激。我不知道如何修复错误，我尝试了无数次。

Error: Could not find the correct Provider above this Builder Widget. This happens because you used a 'BuildContext' that does not include the provider of your choice.

导致错误的相关小部件是消费对话框。此错误涉及 2 个文件。

第一个文件：consumption_dialog.dart

class ConsumptionDialog extends StatefulWidget {
  @override
  _ConsumptionDialogState createState() => _ConsumptionDialogState();
}

class _ConsumptionDialogState extends State<ConsumptionDialog> {
  final _form = GlobalKey<FormState>();
  String? _text;

  String? _validateText(String? value) {
    if (value == null) {
      return "2000 ml minimun";
    }

    final number = int.tryParse(value);
    if (number != null && number >= 2000) {
      return null;
    }

    return "2000 ml minimum";
  }

  @override
  Widget build(BuildContext context) {
    final bloc = context.watch<WaterBloc>();
    return AlertDialog(
      title: Text(
        "Daily consumption",
        textAlign: TextAlign.center,
        style: TextStyle(fontWeight: FontWeight.bold),
      ),
      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(16)),
      content: Form(
        key: _form,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          mainAxisSize: MainAxisSize.min,
          children: [
            Text(
              "Change your daily water consumption goal, in milliliters.",
              textAlign: TextAlign.center,
            ),
            SizedBox(height: 12),
            TextFormField(
              maxLength: 4,
              initialValue: bloc.state.recommendedMilliliters.toString(),
              keyboardType: TextInputType.number,
              onSaved: (value) => _text = value,
              validator: _validateText,
              autovalidateMode: AutovalidateMode.onUserInteraction,
              decoration: InputDecoration(
                hintText: "2000 ml",
                counterText: "",
              ),
            ),
            SizedBox(height: 24),
            PrimaryButton(
              onPressed: () {
                if (_form.currentState?.validate() ?? false) {
                  _form.currentState?.save();
                  FocusScope.of(context).unfocus();
                  context.read<WaterBloc>().setRecommendedMilliliters(
                        int.parse(_text!),
                      );
                  Navigator.of(context).pop();
                }
              },
              title: "Confirm",
            ),
            SizedBox(height: 10),
            SecondaryButton(
              onPressed: () => Navigator.of(context).pop(),
              title: "Cancel",
            ),
          ],
        ),
      ),
    );
  }
}

内联显示错误：

  Widget build(BuildContext context) {
    final bloc = context.watch<WaterBloc>();
    return AlertDialog(

第二个文件：dialog.dart

import 'package:flutter/material.dart';
import 'package:animations/animations.dart';

import 'package:stayhydratedpal/widgets/confirmation_dialog.dart';
import 'package:stayhydratedpal/widgets/consumption_dialog.dart';

Future<bool> showConfirmationDialog(
  BuildContext context, {
  required String title,
  required String content,
}) async {
  final bool confirmed = await showModal(
        context: context,
        builder: (context) {
          return ConfirmationDialog(
            title: title,
            content: content,
            onConfirm: () => Navigator.of(context).pop(true),
            onCancel: () => Navigator.of(context).pop(false),
          );
        },
      ) ??
      false;

  return confirmed;
}

Future<void> showConsumptionDialog(BuildContext context) {
  return showModal(
    context: context,
    builder: (context) => ConsumptionDialog(),
  );
}

内联显示错误：

Future<void> showConsumptionDialog(BuildContext context) {
  return showModal(
    context: context,
    builder: (context) => ConsumptionDialog(),
  );
}

Answer 1

提供程序的工作方式是当您执行 Provider.of<T>(context)（上下文必须是您注入 T 的小部件的后代）时，它会查找树以找到您使用 [=14= 注入的 T ]（可以是 ChangeNotifierProvider 也没关系）。导航器堆栈中的路由也不是彼此的父级他们是

-> page1
-> page2

没有

-> page1
   -> page2

所以这意味着当您使用 Navigator 推送新页面时，Provider 将无法找到您放置在 page1 上的注入提供程序。 showModal 使用 Navigator push 打开一个对话框，所以基本上就像任何其他路线一样，这意味着您的 ConfirmationDialog 没有找到您可能在打开它的页面中注入的 WaterBloc。

解决此问题的一种方法是在 Navigator 上方注入 WaterBloc，MaterialApp 包含根导航器，因此在 Material App 上方注入提供程序。

另一种方法是打开对话框时你可以做

Future<void> showConsumptionDialog(BuildContext context) {
  return showModal(
    context: context,
    builder: (_) => Provider.value(
      value: context.read<WaterBloc>(), // this context must be a descendent of the widget where you injected WaterBloc
      child: ConsumptionDialog(),
    ),
  );
}

一个小技巧，我建议你稍微学习一下 Inherited Widgets，如果你学得好，你可以很容易地使用 Provider，因为 Provider 只是 InheritedWidget 的包装器

ProviderNotFoundException 在构建 ConsumptionDialog 时被抛出，因为使用了不包含提供者的“BuildContext”

ProviderNotFoundException was thrown building ConsumptionDialog because used `BuildContext` that does not include the provider

android

flutter

dart

flutter-provider