I am doing an experiment, where I want to make two similar apps with single source code.
I am trying to make an "adaptive" State on top of the widget tree, and this state (ChangeNotifier) depends on the application (isApp1() determines which app is this ).
here's the code that I'm using:
ChangeNotifierProvider(
create: (context) {
return isApp1() ? AppState1() : AppState2();
},
child: MaterialApp(
onGenerateRoute: isAdminApp()
? App1Router.generateRoute
: App2Router.generateRoute,
initialRoute: "/",
),
);
when I try to read the state using Provider.of in the low levels of the tree I am facing the error:
Error: Could not find the correct Provider<AppState1> above this Widget
Note: when I put AppState1() or AppState2() directly instead of isApp1() ? AppState1() : AppState2() I don't face this error.
Related
I'm building an application that uses lazy internationalization, this way there will be no translation files in the application and all translations will be fetched from the internet when a new page is opened. For that I am using a localization cubit.
Each screen of my application is divided into a "view" that receives the translated messages as a parameter, a "cubit" that contains the cubit screen and its states, and a "container" that contains the BlocProvider for the cubit and the screen.
For now my app starts in the presentation screen, after that it goes to the login screen and finally goes to the home screen.
So in the main file, instead of using the presentation screen directly, I use the localization container and the presentation container comes as its child:
return MaterialApp(
title: 'My App',
theme: myTheme(context),
debugShowCheckedModeBanner: false,
home: LocalizationContainer(
child: PresentationContainer(),
),
);
The PresentationContainer is composed this way:
class PresentationContainer extends BlocContainer {
#override
Widget build(BuildContext context) {
return BlocProvider(
create: (_) => PresentationCubit(),
child: I18NLoadingContainer(
language: BlocProvider.of<CurrentLocaleCubit>(context).state,
viewKey : "Presentation",
creator: (messages) => PresentationView(PresentationViewLazyI18N(messages)),
),
);
}
}
So in the container I have a BlocProvider with PresentationCubit and I18NLoadingContainer as a child.
I18NLoadingContainer just obtains the transalted messages according to the language provided and the screen name, that is "Presentation" in this case. The translated messages are returned in the variable messages, so this messages are passed as parameter to the screen.
If I use this only for my presentation screen everything works fine, but the issue comes when I need to open a new page.
After the presentation screen I need to open the login screen. So in the PresentationView I have the following function when the user clicks the button to open the login screen:
void _goToLogin(BuildContext blocContext) {
Navigator.of(blocContext).pushReplacement(
MaterialPageRoute(
builder: (context) => BlocProvider.value(
value: BlocProvider.of<CurrentLocaleCubit>(blocContext),
child: LoginContainer(),
),
),
);
}
And the LoginContainer works exaclty as the PresentationContainer:
class LoginContainer extends BlocContainer {
#override
Widget build(BuildContext context) {
return BlocProvider(
create: (_) => LoginCubit(),
child: I18NLoadingContainer(
language: BlocProvider.of<CurrentLocaleCubit>(context).state,
viewKey : "Login",
creator: (messages) => LoginView(LoginViewLazyI18N(messages)),
),
);
}
}
If I keep in the presentation screen and use the hot reload everything works fine, but if I open a new screen using this method, I got the following error when try to use hot reload:
The following _CastError was thrown building Builder(dirty): Null
check operator used on a null value
I'm not sure your LoginContainer is still wrapped by the LocalizationContainer when you change the route. I would suggest you to provide a CurrentLocaleCubit above the MaterialApp widget and check whether it's working or not. I think you're loosing a CurrentLocaleCubit instance
I need to pass an argument for my initialRoute. I found this issue and tried it like this:
initialRoute: AuthService.isLoggedIn() ? Views.home : Views.firstStart,
onGenerateInitialRoutes: (String initialRouteName) {
return [
AppRouter.generateRoute(
RouteSettings(
name: AuthService.isLoggedIn() ? Views.home : Views.firstStart,
arguments: notificationPayloadThatLaunchedApp,
),
),
];
},
onGenerateRoute: AppRouter.generateRoute,
This almost works. The problem I have is that somehow after calling this...
Navigator.pushReplacementNamed(
context,
Views.loading,
);
... my Multiprovider which is a parent of my GetMaterialApp is being called again which crashed my app because I call a function when initializing my providers:
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
ChangeNotifierProvider(
create: (context) {
var dataProvider = DataProvider();
dataProvider.init( // <- this is called again which should not happen
context,
);
return dataProvider;
},
),
],
child: GetMaterialApp(
title: 'Flutter Boilerplate',
navigatorKey: Get.key,
initialRoute: AuthService.isLoggedIn() ? Views.home : Views.firstStart,
onGenerateInitialRoutes: (String initialRouteName) {
return [
AppRouter.generateRoute(
RouteSettings(
name: AuthService.isLoggedIn() ? Views.home : Views.firstStart,
arguments: notificationPayloadThatLaunchedApp,
),
),
];
},
onGenerateRoute: AppRouter.generateRoute,
),
);
}
I feel like the way how I pass the initial argument is wrong. Is there any other/better way to get this done? Let me know if you need any more info!
I think you misunderstand the usage of new API onGenerateInitialRoutes cause by the name it should load without the calling of
Navigator.pushReplacementNamed(
context,
Views.loading,
);
API at all. if you call this route from another widget, it means this is already the second route already. it should be the default route for your application. so it makes no sense to give a parameter to an initial route at all.
since you have used Provider Package, it is better to just get whatever argument(parameter) that you want to send via Provider API itself.
if you want to give hardcoded data, then just treat it as a normal Widget class.
home: MyHomePage(name:"parameter name",data:DataHome()), :
GetMaterialApp(
title: 'Flutter Boilerplate',
navigatorKey: Get.key,
home: MyHomePage(name:"parameter name",data:DataHome()),
onGenerateRoute: AppRouter.generateRoute,
);
take note that if you calling Navigator.pushReplacementNamed API . your provider will be gone cause of the Flutter Widget Tree most Navigator API will create a new Widget tree level from the root. since the provider only provides for all its child only. so you cant use any provider data since you have a different ancestor.
so if you only have one page to go I suggest you use the home attribute in MaterialApp API cause it will treat your initial page as a child and Provider API can receive the data cause up in the Widget tree, it has an Ancestor Provider API:
MultiProvider(
providers: [
ChangeNotifierProvider(
if you want to move between pages via navigator after the main page.
consider using NestedNavigator so flutter will not create a new route from the root of the widget tree. so you still can access Provider API's data.
guessing from your variable name. I assume that you want to handle a notification
routing, check this deeplink
I want to share some data across different widgets so I decided to use a ChangeNotifierProvider<Example> with its relative Consumer<Example>. I have already used Providers before but never in this way (in fact I got some errors).
ChangeNotifierProvider<Example> has been defined in menu page while Consumer<Example> in an other widget defined in menu too.
Menu page :
class Menu extends StatefulWidget {
//...SOme code
ChangeNotifierProvider<Example>(
create: (context) => Example(),
child: ShowMultipleAnswers()
//...some code
And now I would like to use Consumer<Example> inside ShowMultipleAnswers() widget consuming data created in menu like :
class ShowMultipleAnswers extends StatefulWidget {
//...some code
Widget build(BuildContext context) {
return Consumer<Example>(builder: (context, handler, child) {
//some code
But I got these errors :
Error: Could not find the correct Provider<Example> above this Consumer<Example> Widget
This happens because you used a `BuildContext` that does not include the provider
of your choice. There are a few common scenarios:
- You added a new provider in your `main.dart` and performed a hot-reload.
To fix, perform a hot-restart.
- 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.
consider using `builder` like so:
Make sure that Consumer<Example> is under your MultiProvider/Provider<Example>.
This usually happens 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>()),
),
}
```
```
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>()),
}
),
}
```
I think the most valid options are 2 :
- The provider you are trying to read is in a different route.
But I don't know because they should be in the same, I mean ShowMultipleAnswers() is the Provider child.
Or the second
- You used a `BuildContext` that is an ancestor of the provider you are trying to read.
In this case, following suggestions above, I should use a builder:(context){} instead of directly calling child : .. but I read that after provider 5 builder has been substituted by create so I'm confused.
If I'm using wrong widgets tell me please!
The error message exactly specifies and describe your error
ShowMultipleAnswers got built using Menu context which doesn't have the Example provider, thus it throws this error.
you can either use builder attribute instead of child or wrap your MaterialApp with the provider
your code should be something like this:
class Menu extends StatefulWidget {
//...SOme code
ChangeNotifierProvider<Example>(
create: (context) => Example(),
builder: (context) {
return ShowMultipleAnswers();
}
//...some code
I forgot to say that there was an other page between Menu and ShowMultipleAnswers, like a bridge between them so the real flow was :
Menu Page -> Bridge Page -> ShowMultipleAnswers Page.
I removed this Bridge Page and it worked! But I still don't understand why it didn't work, maybe because Bridge Page didn't have any references of its Provider?
The issue is that I don't get any values out of my StreamProviders (which are defined on a global level) within my Authenticated route:
runApp(MultiProvider(
providers: [
Provider.value(value: userService),
StreamProvider.value(value: authService.userStream, initialData: null),
StreamProvider.value(value: userService.userDataStream),
StreamProvider.value(value: userService.characterStream),
],
child: MyApp(),
));
}
I noticed that it's to do with the logic that I have for my Navigator (if I remove it the provider values are passed down the widget tree as expected). The Navigator I'm using is based around the idea that the app has 3 states: Not Authenticated, Authenticated and Authenticated-First-Time. I get the value whether I'm authenticated from the loginStream (so far everything works):
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: loginStream,
builder: (ctx, snapshot) {
if (!snapshot.hasData) return Loading();
LoginState state = snapshot.data;
if (state == LoginState.LOGGED_OUT) return LoginScreen();
if (state == LoginState.FIRST_TIME) return CharacterCreationScreen();
return Navigator(
key: navigatorKey,
initialRoute: "/home",
onGenerateRoute: (settings) => PageRouteBuilder(
pageBuilder: (ctx, _, __) => routes(settings)(ctx),
transitionsBuilder: pageTransition,
),
);
},
);
The thing is that if I'm Authenticated and say in the HomeScreen, then both userDataStream and characterStream return null even if there's actual data available. If I remove the StreamBuilder + LoginLogic itself and just have the Navigator widget returned above, then HomeScreen gets the correct values.
UPDATE:
I noticed that it's not even the StreamBuilder. If I remove the 3 if's within the builder, then the stream values are propagated correctly. Not sure why that happens.
I´m not quite sure if this helps since I´m lacking details but here is what I noticed so far:
If you create the objects in the multiprovider for the first time you should not use .value - check if this applies.
Try cleaning up the if statements in the function body of your StreamBuilder (use if, else if and else keywords.
Also, following your description, it sounds like whenever an if statement is true, returns and thus cancels the build´s function body, the stream somehow resets and defaults to null. Maybe look into that & update your question.
Change this
Provider.value(value: userService),
StreamProvider.value(value: authService.userStream, initialData: null),
To this
Provider(create: (context) => userService)
StreamProvider(create:(context) => authService.userStream, initialData: null),
Do the same for all the providers that u are registering
To expose a newly created object, use the default constructor of a provider. Do not use the .value constructor if you want to create an object, or you may otherwise have undesired side effects.
https://pub.dev/packages/provider
I am not able to set localization in my app.
I am trying to add language settings and associated localization in my app. I am able to get-set the language option. I am using 'intl' plug-in for internationalization. My code looks like below in pretty much all the UI .dart files.
AppTranslations.of(context).accountNumber +
" ${accountDetails.accountNumber}",
The getters is set as :
String get accountNumber => _text("account_number");
String _text(String key) {
return _localisedValues[key] ?? _defaultLocaleValues[key];
}
I've also placed json files containing localized labels in 3 different languages. However, it seems there is some instantiation problem of the locazation plug-in. The code doesn't go the getter line.
Any help would be highly appreciated.
AppTranslations.of(context) is a standard way of accessing the localised labels. You are right about the instantiation. If the program doesn't go to the getter line them it means, there's a problem in somewhere in the initial part of the code. It could be in the main.dart.
Check where you are initialising LocalStorageProvider(). In case it is not initialised then that's the problem. Assuming you are using a MaterialApp, try the below suggestion then :
Wrap the MaterialApp with LocalStorageProvider(). I mean, in the main widget build, return LocalStorageProvider() and pass your existing code of MaterialApp() as a child to it. Sample below (Please ignore the theme etc since I just copied the code from one of my app) :
#override
Widget build(BuildContext context) {
LocalStorage localStorage = LocalStorage();
return LocalStorageProvider(
localStorage: localStorage,
child: LocaleProvider(
localStorage: localStorage,
localeWrapper: LocaleWrapper(),
child: Builder(
builder: (context) {
return AnimatedBuilder(
animation: LocaleProvider.of(context).localeWrapper,
builder: (context, _) {
return MaterialApp(
onGenerateTitle: (context) =>
AppTranslations.of(context).appName,
locale: LocaleProvider.of(context).locale,
title: "App Title",
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MapsDemo(),
localizationsDelegates: [
AppTranslationsDelegate(
LocaleProvider.of(context).supportedLanguagesCodes,
),
GlobalMaterialLocalizations.delegate,
GlobalWidgetsLocalizations.delegate,
],
supportedLocales: LocaleProvider.of(context).supportedLocales,
);
},
);
},
),
),
);
}