我正在Flutter上开发一个应用程序（我仍然还是一个新手），但遇到以下错误：
Error: Could not find the correct Provider<List<Category>> above this Exercises Widget
This likely happens because you used a `BuildContext` that does not include the provider
of your choice. There are a few common scenarios:
- The provider you are trying to read is in a different route.
Providers are "scoped". So if you insert of provider inside a route, then
other routes will not be able to access that provider.
- You used a `BuildContext` that is an ancestor of the provider you are trying to read.
Make sure that Exercises is under your MultiProvider/Provider<List<Category>>.
This usually happen when you are creating a provider and trying to read it immediately.
For example, instead of:
```
Widget build(BuildContext context) {
return Provider<Example>(
create: (_) => Example(),
// Will throw a ProviderNotFoundError, because `context` is associated
// to the widget that is the parent of `Provider<Example>`
child: Text(context.watch<Example>()),
),
}
```
consider using `builder` like so:
```
Widget build(BuildContext context) {
return Provider<Example>(
create: (_) => Example(),
// we use `builder` to obtain a new `BuildContext` that has access to the provider
builder: (context) {
// No longer throws
return Text(context.watch<Example>()),
}
),
我一直在网上寻找，这显然与我在exercises_add.dart中调用Provider.of >（context）时无法获得正确的“ context”有关，而我没有真的不明白为什么。因为如您在我的Exercises.dart中看到的那样，我有一个“ body：exerciseList（）”，在其中我可以从StreamProvider中获取类别，但是当我尝试通过单击“ floatingActionButton”然后尝试访问它时打开我的ExerciseAdd（）页面，它将引发该错误。
我非常感谢一个解决方案（+说明），该解决方案涉及如何修复我的代码以及为什么不起作用。
exercises.dart
Widget build(BuildContext context) {
return _isLoading
? Loading()
: MultiProvider(
providers: [
StreamProvider<List<Exercise>>(
create: (context) => DatabaseService().exercises,
),
StreamProvider<List<Category>>(
create: (context) => DatabaseService().categories,
),
ChangeNotifierProvider<ExerciseFilter>(
create: (context) => ExerciseFilter(isActive: true),
)
],
child: Scaffold(
appBar: AppBar(
title: Text('Exercises'),
elevation: 0.0,
actions: _buildActions(),
),
body: ExerciseList(),
floatingActionButton: FloatingActionButton(
backgroundColor: Colors.black,
child: Icon(Icons.add, color: Colors.white),
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ExercisesAdd(),
),
);
},
),
),
);
}
}
exercises_add.dart
@override
Widget build(BuildContext context) {
final cats = Provider.of<List<Category>>(context);
print(cats.length);
return Scaffold(
appBar: AppBar(
title: Text('Add Exercise'),
elevation: 0.0,
),
body: SingleChildScrollView(
child: Container(
padding: EdgeInsets.symmetric(vertical: 20.0, horizontal: 50.0),
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
SizedBox(height: 20.0),
TextFormField(
decoration:
textInputDecoration.copyWith(hintText: 'Exercise Name'),
validator: (value) {
if (value.isEmpty) {
return 'Exercise name is required';
}
return null;
},
onChanged: (value) {
setState(() {
exerciseName = value;
});
},
),
SizedBox(height: 20.0),
Theme(
data: Theme.of(context).copyWith(canvasColor: Colors.white),
child: DropdownButtonFormField<String>(
decoration: dropdownDecoration,
value: exerciseCategory,
onChanged: (value) {
setState(() {
exerciseCategory = value;
});
},
items: categories.map<DropdownMenuItem<String>>((value) {
return DropdownMenuItem<String>(
value: value.name,
child: Text(value.name),
);
}).toList(),
),
),
SizedBox(height: 20.0),
RaisedButton(
elevation: 0,
color: Colors.black,
child: Text(
'Add Exercise',
style: TextStyle(color: Colors.white),
),
onPressed: () async {
if (_formKey.currentState.validate()) {
bool failed = false;
String uid = await _auth.getCurrentUser();
if (uid != null) {
dynamic result = DatabaseService(uid: uid)
.addExercise(exerciseName, exerciseCategory);
if (result != null) {
Navigator.pop(context);
} else {
failed = true;
}
} else {
failed = true;
}
if (failed) {
setState(() {
error = 'Failed to add exercise. Please try again';
});
}
}
},
),
SizedBox(height: 12.0),
Text(
error,
style: TextStyle(color: Colors.red, fontSize: 14.0),
),
],
),
),
),
),
);
DatabaseService（）。exercises
List<Category> _categoryListFromSnapshot(QuerySnapshot snapshot) {
return snapshot.documents.map((doc) {
return Category(name: doc.data['category'] ?? '');
}).toList();
}
Stream<List<Category>> get categories {
return categoryCollection
.orderBy('category')
.snapshots()
.map(_categoryListFromSnapshot);
}
注意：StreamProvider和MultiProvider等都是“提供商”包的一部分（我使用的是最新版本）
答案 0 :(得分：0)
您收到的错误描述了您当前所处的场景。
-您尝试读取的提供程序处于不同的路径。
提供者是“范围”的。因此，如果您在路由内插入提供商， 那么其他路由将无法访问该提供商。
您正在导航到其他路由并尝试访问提供程序，但是它不再在小部件树中。
您只需要将MultiProvider移动到小部件树中正在使用的任何导航器上方。您可能使用MaterialApp来执行此操作，因此移动MultiProvider并将MaterialApp设置为child。