I have four providers, that all provide the Instances of Challenge class, to the same Widget.
They are different challenges, but I don't know how to differentiate between the providers, so i wondered, if it's possible to give names to the providers.
Actually, you can't, this is the biggest drawback of provider, you can use riverpod instead, it's from the same author, but it has some advantages over a normal provider.
this is what the author of both provider and riverpod sais.
It makes the provider pattern more flexible, which allows supporting commonly requested features like:
Being able to have multiple providers of the same type.
No. While you can have multiple providers sharing the same type, a widget will be able to obtain only one of them: the closest ancestor.
Instead, you must explicitly give both providers a different type.
Instead of:
Provider<Challenge>(
create: (_) => 'Something',
child: Provider<Challenge>(
create: (_) => 'SomethingElse',
child: ...,
),
),
Prefer:
MultiProvider(
providers: [
Provider<ChallengeOne>(create: (_) => Something()),
Provider<ChallengeTwo>(create: (_) => SomethingElse()),
Provider<ChallengeThree>(create: (_) => AnotherThing()),
],
child: someWidget,
)
Related
I got this error:
'ChangeNotifierProvider' isn't a function. Try correcting the name to
match an existing function, or define a method or function named
'ChangeNotifierProvider'
I'm looking to migrate provider to Riverpod, but it is difficult for me to do that
This is my code:
void main() async {
await Hive.initFlutter();
await Hive.openBox("Habit_Database");
runApp(MultiProvider(providers: [
ChangeNotifierProvider(
create: (context) => UserProvider(),
),
], child: const MyApp()));
}
How can I solve this issue?
Thanks for any help you can provide
I'm working on this right now for a client. I have chosen to maintain the existing provider infrastructure while slowly migrating one provider at a time to riverpod.
To make this work, I first constructed a renaming shim for all of the exported provider functions. It imports provider, and establishes typedefs to alias those names to universally end in "X", including the extension on BlockContext which becomes .readX and .selectX. I tested this by not having the "X" initially, then renaming each symbol in VSC one at a time, which surprisingly worked well. The renaming shim looks something like:
import 'package:provider/provider.dart' as provider;
typedef ProviderX<T> = provider.Provider<T>;
typedef MultiProviderX = provider.MultiProvider;
typedef ChangeNotifierProviderX<T extends ChangeNotifier> = provider.ChangeNotifierProvider<T>;
which continues for about 100 lines. The tricky ones are the extensions:
extension ReadContext on BuildContext {
T readX<T>() => provider.ReadContext(this).read<T>();
}
extension SelectContext on BuildContext {
R selectX<T, R>(R Function(T value) selector) => provider.SelectContext(this).select(selector);
}
Admittedly, once I started the pattern, Github copilot eagerly offered me line after line, and was wrong for only a few things initially.
Next, I added the RiverPod ProviderScope to my runApp, and selected a particular provider to migrate. I created the equivalent in RiverPod, nicely namespaced because "FooProvider" became "fooProvider", and then located all references to that class in .readX or ConsumerX access. I inserted the equivalent with Consumer blocks or ConsumerWidget widgets, giving me a ref to use with ref.read or ref.watch as appropriate.
It's not trivial. But once you get over "the great rename" hurdle, the rest is just a rather mechanical translation, and can be done incrementally.
The error message is indicating that ChangeNotifierProvider isn't a function. You are trying to migrate from provider to Riverpod.
In Riverpod, the equivalent class for ChangeNotifierProvider is ChangeNotifierProvider.autoDispose.
So you should replace this line:
ChangeNotifierProvider(
create: (context) =>
UserProvider(),
),
with this line:
ChangeNotifierProvider.autoDispose( create: (context) => UserProvider(),),
This should solve the issue.
I'm using Flutter provider, and I want to access a provider from another provider without using context.
I found many documentations on the internet explaining how to use ProxyProvider, but no one of the implementations was working (I think it's related to the last update 3 months ago).
I posted this question in StackOverflow after encountering a problem in ProxyProvider, but I didn't get an answer.
So now I'm just searching for any way to use a provider inside another one without using context.
You mean a Provider or the service that the Provider encapsulates? If it's the latter, the way that I've done it is by calling a provided service inside another provided service, given that they are all under the same MultiProvider. For example, I have two provided services:
MultiProvider(
providers: [
ChangeNotifierProvider(
create: (_) => FirstService()
),
ChangeNotifierProvider(
create: (_) => SecondService()
),
]
)
FirstService looks like this:
class FirstService extends ChangeNotifier {
List<String> getListOfValues() {
return ['a', 'b', 'c'];
}
}
and for example, I need to access those values from the SecondService, then I do this:
class SecondService extends ChangeNotifier {
void pullDataFromService(BuildContext context) {
FirstService firstService = Provider.of<FirstService>(context, listen: false);
var values = firstService.getListOfValues();
}
}
So pretty much you pass a context to a method where you need to access a provided service and you extract it from the Provider as normal, then access its functionality from the other service where you fetch it.
For my flutter project, I am using the following multiple providers below:
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
ChangeNotifierProvider<FirstProvider>(
create: (context) => FirstProvider(),
),
ChangeNotifierProvider<SecondProvider>(
create: (context) => SecondProvider(),
),
ChangeNotifierProvider<ThirdProvider>(
create: (context) => ThirdProvider(),
),
ChangeNotifierProvider<FourthProvider>(
create: (context) => FourthProvider(),
),
],
child: const MainApp(),
);
}
Because sometimes I need to either get data or call functions from different providers from another provider, I am using it like this:
//First Provider
class FirstProvider with ChangeNotifier {
void callFunctionFromSecondProvider({
required BuildContext context,
}) {
//Access the SecondProvider
final secondProvider= Provider.of<SecondProvider>(
context,
listen: false,
);
secondProvider.myFunction();
}
}
//Second Provider
class SecondProvider with ChangeNotifier {
bool _currentValue = true;
void myFunction(){
//Do something
}
}
The callFunctionFromSecondProvider()of the FirstProvider is called from a widget and it will call myFunction() successfully, most of times.
Depending on the complexity of the function, I am sometimes experiencing that I can't access the SecondProvider, presumably due to context being null, when the widget state changes.
I am reading some documents online regarding provider, and they are suggesting changenotifierproxyprovider for what I understood as 1 to 1 provider relationship.
However, in my case, one provider needs to be accessed by multiple providers and vice versa.
Question:
Is there a more appropriate way that I can approach my case where one provider can be accessed by multiple providers?
EDIT:
Accessing provider should also be able to access different variable values without creating a new instance.
Instead of passing context to the callFunctionFromSecondProvider function add the second provider as the parameter. So the function looks like the below.
Not sure this is the correct way of doing that but my context null issue was fixed this way.
void callFunctionFromSecondProvider({
required SecondProvider secondProvider,
}) {
secondProvider.myFunction();
}
}
Alright.
So it looks like Riverpod by the same author is the way to go as it addresses alot of flaws such as Provider being dependent on the widget tree, in my case, where the underlying issue came from.
—--------
For the time being, I still need to use the provider and for a quick and dirty solution, I am providing the context of not only the current widget that I am trying to access the provider, but also passing the parent context of the widget directly, so that in case a modal (for example) is closed, then any subsequent provider call can still be executed using the parent context.
Hope this helps.
In main.dart file I always have to add the same thing with different class name to make things works, here is an example.
MultiProvider(
providers: [
ChangeNotifierProvider<ProductDataProvider>(
create: (_) => ProductDataProvider()),
ChangeNotifierProvider<AuthenticationProvider>(
create: (_) => AuthenticationProvider()),
],
child: Container())
If we have 20 providers let's say then there is a lot duplicate code there right. Is any work around this?
See, if it is about initializing your provider in your main.dart, I am afraid, you have to do it, cos it need those.
For any duplicates, you can make use of some short tricks and get going.
Create an Array consisting of all your ChangeNotifiers, like in this case: ProductDataProvider and AuthenticationProvider
List<ChangeNotifier>_providersArray = [ProductDataProvider, AuthenticationProvider];
Now, when you have the array, add it to the array which adds the ChangeNotifier, to your final providers list.
// This will be your array of Providers, which you will add to Mutliprovider(providers: HERE)
List<Provider> providers = []; // make sure you have the right type of the List<>, which the `providers` in `Multiproviders` accepts
for(var provider in _providersArray){
//adding the provider name to the ChangeNotifier
providers.add(ChangeNotifierProvider<provider>( create: (_) => provider()));
}
Finally passing the providers in your Multiprovider
MultiProvider(
providers: providers,
child: Container()
)
Max to max, you will have to do the type casting for some type mismatches, and you're good to go. Let me know if that helps you in anyway.
I have a ChangeNotifier, and I would like to share it between multiple routes but not all routes:
Page1 is my first page. I need share data of ChangeNotifierProvider with Page2, Page3 and Page only and on enter Page1 call dispose of my ChangeNotifierProvider.
How can I do this using provider?
To do so, the easiest solution is to have one provider per route, such that instead of:
Provider(
builder: (_) => SomeValue(),
child: MaterialApp(),
)
you have:
final value = SomeValue();
MaterialApp(
routes: {
'/foo': (_) => Provider.value(value: value, child: Foo()),
'/bar': (_) => Provider.value(value: value, child: Bar()),
'/cannot-access-provider': (_) => CannotAccessProvider(),
}
)
It is, on the other hand, not possible to have your model "automatically disposed".
provider is not able in such a situation to know that it is safe to dispose of the object.