Flutter: Refresh parent widget on Navigation.pop - flutter

I have a parent widget "BookmarkedShows" and child widget "ListOfShows". From child widget, when user taps on list item, it opens details page. When the user removes the show from bookmark from details page, on pressing back button, the show is not removed from the listing page. ie the parent is not refreshed. I'm using BlocBuilder.
There are some options mentioned in other question to add .then() to Navigator.push() method. However Navigator.push() happens in children component. How would I force refresh parent BlocBuilder during Navigation.pop()?
Parent "BookmarkedShows":
class BookmarkedShows extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BlocProvider(
create: (context) => BookmarkShowsBloc()..add(LoadBookmarkedShows()),
child: BlocBuilder<BookmarkShowsBloc, BookmarkedShowsState>(
builder: (BuildContext context, BookmarkedShowsState state) {
return ShowList("Bookmarked shows", state.shows)
}),
);
}
}
Child "ListOfShows":
class ListOfShows extends StatelessWidget {
final String listName;
final List<Show> shows;
const ListOfShows(this.listName, this.shows);
#override
Widget build(BuildContext context) {
return Wrap(children: shows.map((show) => showItem(show, context)).toList());
}
InkWell showItem(Show show, BuildContext context) {
return InkWell(
onTap: () async {
await Navigator.of(context).push(MaterialPageRoute(
builder: (context) => showDetails(show)));
},
child: Container(
CachedNetworkImage(
imageUrl: show.portraitPoster
),
));
}
}

The question stated is a bit unclear, but I'm going to answer it the best I can.
If you want your widget to be able to update you need to make it Stateful.
Make your BookmarkedShows Widget Stateful:
class BookmarkedShows extends StatefulWidget {
BookmarkedShows ({Key key}) : super(key: key); //Can also work without this line
#override
StatefulBookmarkedShows createState() => StatefulBookmarkedShows();
}
class StatefulBookmarkedShows extends State<BookmarkedShows> {
#override
Widget build(BuildContext context) {
return BlocProvider(
create: (context) => BookmarkShowsBloc()..add(LoadBookmarkedShows()),
child: BlocBuilder<BookmarkShowsBloc, BookmarkedShowsState>(
builder: (BuildContext context, BookmarkedShowsState state) {
return ShowList("Bookmarked shows", state.shows)
}),
);
}
}
On returning back to parent you could implement something like in this Flutter docs example which might help to update the parent when navigating back. The async method awaits a response back from the child(Navigator).
When returning back to the Stateful parent you can call this like in the above mentioned async method:
LoadBookmarkedShows();
setState(() { });
I hope it works. Goodluck.

Related

Consumer and context.watch in MultiProvider

I am trying Flutter for the first time, and I am a little confused by the MultiProvider class.
The question is straightforward, but I didn't find an explanation:
when should one use Consumer and when context.watch?
For instance, taking one of the examples apps I have found, I tried using two providers for two global states, the theme and the status of the app:
runApp(
MultiProvider(providers: [
ChangeNotifierProvider(create: (context) => AppTheme()),
ChangeNotifierProvider(create: (context) => AppStatus()),
],
child: const MyApp()
));
Then the app widget accesses the theme with Consumer:
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Consumer<AppTheme>(
builder: (context, appTheme, child) {
// ...
As far as I understand, now all children widgets will inherit the provider. Is it right?
My home page, then, called by the MyApp class does not use Consumer, but context.watch:
#override
Widget build(BuildContext context) {
final appTheme = context.watch<AppTheme>();
final appStatus = context.watch<AppStatus>();
return NavigationView(
// ...
It works, don't get me wrong, but I just copied the row above my appStatus, so I don't really fully understand it. This is also due to another screen that I've concocted to access the AppStatus global state, but I use Consumer, as suggested by the Flutter documentation:
class _ViewerState extends State<Viewer> {
#override
Widget build(BuildContext context) {
return Consumer<AppStatus>(
builder: (context, appStatus, child) {
return ScaffoldPage.scrollable(
header: const PageHeader(title: Text('Test')),
children: [
FilledButton(child: Text("Try ${appStatus.count}"), onPressed: (){ appStatus.increment(); debugPrint('pressed ${appStatus.count}'); }),
FilledButton(child: Text("Reset"), onPressed: (){ appStatus.reset(); }),
]);
},
);
}
}
I have the feeling that I am misusing something here, and I do not really understand what's going on under the hood...
context.watch<T>() and Consumer<T> does the same thing. Most of the time context.watch<T>() is just more convenient. In some cases where context is not available Consumer<T> is useful.

Getx argumentsbeing cleared after using showDialog() in Flutter

The used Getx Arguments are cleared after the showDialog method is executed.
_someMethod (BuildContext context) async {
print(Get.arguments['myVariable'].toString()); // Value is available at this stage
await showDialog(
context: context,
builder: (context) => new AlertDialog(
//Simple logic to select between two buttons
); // get some Confirmation to execute some logic
print(Get.arguments['myVariable'].toString()); // Variable is lost and an error is thrown
Also I would like to know how to use Getx to show snackbars without losing the previous arguments as above.
One way to do this is to duplicate the data into a variable inside the controller and make a use from it instead of directly using it from the Get.arguments, so when the widget tree rebuild, the state are kept.
Example
class MyController extends GetxController {
final myArgument = ''.obs;
#override
void onInit() {
myArgument(Get.arguments['myVariable'] as String);
super.onInit();
}
}
class MyView extends GetView<MyController> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Expanded(
child: Center(child: Obx(() => Text(controller.myArgument()))),
),
);
}
}
UPDATE
Since you are looking for solution without page transition, another way to achieve that is to make a function in the Controller or directly assign in from the UI. Like so...
class MyController extends GetxController {
final myArgument = 'empty'.obs;
}
class MyView extends GetView<MyController> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Expanded(
child: ElevatedButton(
onPressed: () => _someMethod(context),
child: Obx(() => Text(controller.myArgument())),
),
),
);
}
void _someMethod(BuildContext context) async {
// store it in the state.
controller.myArgument(Get.arguments['myVariable'] as String);
await showDialog(
context: context,
builder: (context) => new AlertDialog(...),
);
print(controller.myArgument()); // This should work
}
}
UPDATE 2 (If you don't use GetView)
class MyController extends GetxController {
final myArgument = 'empty'.obs;
}
class MyView extends StatelessWidget {
final controller = Get.put(MyController());
#override
Widget build(BuildContext context) {
return Scaffold(
body: Expanded(
child: ElevatedButton(
onPressed: () => _someMethod(context),
child: Obx(() => Text(controller.myArgument())),
),
),
);
}
void _someMethod(BuildContext context) async {
// store it in the state.
controller.myArgument(Get.arguments['myVariable'] as String);
await showDialog(
context: context,
builder: (context) => new AlertDialog(...),
);
print(controller.myArgument()); // This should work
}
}
UPDATE 3 (NOT RECOMMENDED)
If you really really really want to avoid using Controller at any cost, you can assign it to a normal variable in a StatefulWidget, although I do not recommend this approach since it was considered bad practice and violates the goal of the framework itself and might confuse your team in the future.
class MyPage extends StatefulWidget {
const MyPage({ Key? key }) : super(key: key);
#override
_MyPageState createState() => _MyPageState();
}
class _MyPageState extends State<MyPage> {
String _myArgument = 'empty';
#override
Widget build(BuildContext context) {
return Scaffold(
body: Expanded(
child: ElevatedButton(
onPressed: () => _someMethod(context),
child: Text(_myArgument),
),
),
);
}
void _someMethod(BuildContext context) async {
// store it in the state.
setState(() {
_myArgument = Get.arguments['myVariable'] as String;
});
await showDialog(
context: context,
builder: (context) => new AlertDialog(...),
);
print(_myArgument); // This should work
}
}

Flutter - Cant find bloc in the parent tree when using showDialog

Im using Flutter and flutter_bloc for a small app, and i used MultiBlocProvider to use multiple BlocProviders that i need in the main home page, and under the home page, there is a MainWidget, which can access the given Bloc easily by: BlocProvider.of<OldBloc>(context)
The MainWidget calls NewWidget as a dialog by: showDialog(context: context, builder: (context) => NewWidget())
The problem is, i cannot access OldBloc from NewWidget(), so i assumed that MainWidget isnt passing its context to NewWidget when using showDialog ?
HomeScreen.dart
import 'package:flutter/material.dart';
class HomeScreen extends StatelessWidget {
const HomeScreen({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
body: MultiBlocProvider(
providers: [
BlocProvider(
create: (context) => OldBloc()..add(Initialize()),
),
BlocProvider(
create: (context) => OtherBloc()..add(Initialize()),
),
],
child: Stack(
children: [
MainWidget(),
MenuWidget(),
],
),
));
}
}
MainWidget.dart
import 'package:flutter/material.dart';
class MainWidget extends StatelessWidget {
const MainWidget({
Key key,
}) : super(key: key);
#override
Widget build(BuildContext context) {
return TextField(onTap: () => showDialog(context: context, builder: (context) => NewWidget()));
}
}
NewWidget.dart
import 'package:flutter/material.dart';
class NewWidget extends StatelessWidget {
const NewWidget({Key key}) : super(key: key);
#override
Widget build(context) {
return Text(BlocProvider.of<OldBloc>(context).name); // <------- THIS GIVES AN ERROR THAT IT CANT FIND A BLOC OF THE TYPE OldBloc
}
}
You can simply use this (suggested by Flex Angelov):
showDialog(
context: superContext,
builder: (_) {
return BlocProvider.value(
value: superContext.read<MyBloc>(),
child: const MyDialogWidget(),
);
},
);
and make sure superContext has access to your BLoC.
You have no access to BuildContext in your showDialog method, documentation:
The widget returned by the builder does not share a context with the location that showDialog is originally called from.
The context argument is used to look up the Navigator and Theme for the dialog. It is only used when the method is called.
Its also recommended to use a StatefulBuilder or a custom StatefulWidget, here is an example.
I solved this problem.
I use cubit instead of bloc but it doesn't matter.
ShowDialog doesn't pass parent context. So you should create a new cubit and pass your parent cubit and state in arguments for a new cubit. I called main cubit FooCubit, new cubit FooCubitWrapper and DialogWidget is child widget that needs some BLOC logic in showDialog.
var fooCubit = context.read<FooCubit>(); // your parrent cubit and state
return BlocBuilder<FooCubit , FooState>(
builder: (_, state) {
.
.///some logic///
.
showDialog(
context: context,
builder: (_) => // here you have to create new cubit
BlocProvider( // because there is no access to parent cubit
create: (_) => FooCubitWrapper(cubit, state),
child: DialogWidget(),
),
);
This is FooCubitWrapper. For example, we need the boo method from the parent cubit. So we need to create here boo method and inside we need to reference to parent boo method and emit parent state.
class FooCubitWrapper extends Cubit<FooState> {
FooCubit fooCubit;
FooCubitWrapper(this.fooCubit, FooState initialState) : super(initialState);
boo() {
fooCubit.boo();
emit(fooCubit.state);
}
}
And finally, in your DialogWidget, you do all like usual
var cubit = context.read<TagsCubitWrapper>();
return BlocBuilder<TagsCubitWrapper, TagsState>(
builder: (context, state) {
// work with methods and fields as usual
cubit.boo();
if !(state.someField) {}
});

Flutter: can't access Provider from showModalBottomSheet

I can't access a provider defined above a Scaffold from showModalBottomSheet in the FloatingActionButton.
I've defined a HomePage like so:
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => MyProvider(),
builder: (context, _) {
return Scaffold(
body: Consumer<MyProvider>(
builder: (context, provider, _) {
return Text(provider.mytext); // this works fine
}
),
floatingActionButton: MyFAB(), // here is the problem
);
}
)
}
}
And this is MyFAB:
class MyFAB extends StatefulWidget {
#override
_MyFABState createState() => _MyFABState();
}
class _MyFABState extends State<MyFAB> {
#override
Widget build(BuildContext context) {
return FloatingActionButton(
...
onPressed: () => show(),
);
}
void show() {
showModalBottomSheet(
...
context: context,
builder: (BuildContext context) {
return Wrap(
children: [
...
FlatButton(
onPressed: Provider.of<MyProvider>(context, listen: false).doSomething(); //Can't do this
Navigator.pop(context);
)
],
);
}
);
}
}
Error: Could not find the correct Provider<MyProvider above this BottomSheet Widget.
Fixed by placing the provider above MaterialApp, as described here.
Bottom sheets are created at the root of the material app. If a prodiver is declared below the material app, a bottom sheet cannot access it because the provider is not an ancestor of the bottom sheet in the widget tree.
The screenshot below shows a widget tree: the whole app is inside Wrapper and the bottom sheet is not created inside Wrapper. It is created as another child of MaterialApp (with a root element Container in this case).
For your case:
// main.dart
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => MyProvider(),
builder: (context, _) {
return MaterialApp(
home: HomePage(),
);
},
);
}
}
// home_page.dart
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: MyFAB()
);
}
}
This is caused by passing it the wrong context. Wrap your FAB to a Builder widget and pass it as builder property. This will take a new context and pass it to showModalBottomSheet. Also, you can do onPressed: show, it's more concise.
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => MyProvider(),
builder: (context, _) {
return Scaffold(
body: Consumer<MyProvider>(
builder: (context, provider, _) {
return Text(provider.mytext); // this works fine
}
),
floatingActionButton: MyFAB(context), // here is the problem
);
}
)
}
}
class MyFAB extends StatefulWidget {
#override
_MyFABState createState() => _MyFABState();
}
class _MyFABState extends State<MyFAB> {
#override
Widget build(BuildContext context) {
return FloatingActionButton(
...
onPressed: (context) => show(context),
);
}
void show(ctx) {
showModalBottomSheet(
...
context: ctx,
builder: (BuildContext context) {
return Wrap(
children: [
...
FlatButton(
onPressed: () {
Provider.of<MyProvider>(ctx, listen: false).doSomething(); //Can't do this
Navigator.pop(ctx)
};
)
],
);
}
);
}
}
SOLUTION
HomePage:
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => MyProvider(),
builder: (context, _) {
return Scaffold(
body: Consumer<MyProvider>(
builder: (context, provider, _) {
return Text(provider.mytext); // this works fine
}
),
floatingActionButton: MyFAB(context), // here is the problem
);
}
)
}
}
MyFAB:
class MyFAB extends StatefulWidget {
final BuildContext ctx;
MyFAB(this.ctx)
#override
_MyFABState createState() => _MyFABState();
}
class _MyFABState extends State<MyFAB> {
#override
Widget build(BuildContext context) {
return FloatingActionButton(
...
onPressed: () => show(),
);
}
void show() {
showModalBottomSheet(
...
context: context,
builder: (BuildContext context) {
return Wrap(
children: [
...
FlatButton(
onPressed: Provider.of<MyProvider>(widget.ctx, listen: false).doSomething(); //Can't do this
Navigator.pop(context);
)
],
);
}
);
}
}
In my opinion: showModalBottomSheet builds a bottom sheet with context which comes from Material App
1st image
so when we return any Widget to show in the Bottom sheet it uses that Material app context as we can see in the builder property in the:1st image.
2ng Image: your code
so in your code, when you are writing: Provider.of(context, listen: false).doSomething(); it is using context from the builder: (BuildContext context) which is the context of Material App. we have to change this context in order to use this Provider without having to uplift the position of our Provider above the Material App.
Now if we want to keep using that context to get the benefits of that overlay and automatic detection of suitable themes and still want to use the context of a widget that does have access to our provider:
we can pass the context of the Widget which does have Provider access to the FAB, but we will have to keep passing that context through widgets till we need to use that Provider in our FAB or till we go to a different route: in which case we can start from a new context and provider as Providers are scoped in mature.
so in your HomePage either you can wrap your scaffold inside a Builder or you can create a new widget like this:"
3rd image
so that it will have its own context which does have access to the provider we need inside our FAB as shown below in 4th image:
4th image
and then in the builder property of showModalBottomSheet change the name of the parameter in an anonymous function so that it won't be confused with the MAterial App context and context we will be passing in (Builder context or IdeaScreen context in my case image 4th)
5th image
I am creating a new widget but you do not have need to do so you can directly write your Fab code inside the anonymous function:
and can use context(not newContext which is related to Material App context) while calling the Provider as you are already doing.
But I will show in my case What I am doing in my AddTask Widget in case anyone's use case is similar to mine:
6th image
expect a context, which does have a provider access, I my case its context of IdeaScreen.
and then use it just like this:
7th image

How to navigate to another page on load in Flutter

I want to navigate to the login page if there is no logged in user, otherwise display the homepage. I thought of calling Navigator.of(context).push() conditionally inside the build method but that triggers an exception. Is there some method I'm missing that I can override?
Update to add the Homepage widget
class HomePage extends StatelessWidget {
final AppUser user;
const HomePage({Key key, this.user}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Rera Farm'),
actions: <Widget>[
PopupMenuButton(
itemBuilder: (BuildContext context) {
return <PopupMenuEntry>[
PopupMenuItem(
child: ListTile(
title: Text('Settings'),
onTap: () {
Navigator.pop(context);
Navigator.push(context,
MaterialPageRoute(builder: (BuildContext context)
=> SettingsPage()
));
},
),
),
];
},
)
],
),
body: _buildBody(context));
}
And the container
class HomePageContainer extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new StoreConnector<AppState, _ViewModel>(
converter: _ViewModel.fromStore,
builder: (BuildContext context, _ViewModel vm) {
return HomePage(
user: vm.user,
);
},
);
}
}
You need to either use a ternary in the onTap if you're using the settings button or, if you just want it to automatically send the user to the correct page when the app starts, you can put the ternary in the MyApp build method.
If you are using the settings button and just want it to pop back to the previous page if the person is not logged in then you can change NotLoggedIn() to a pop.
For some strange reason SO is refusing to post the code when it is properly formatted with four spaces, exactly as it asks, so I'm just going to make a gist.
https://gist.github.com/ScottS2017/3288c7e7e9a014430e56dd6be4c259ab
Here's how I end up doing it. I do the checks in the main method, so the user sees the splash screen set in manifest while those weird checks are made:
void main() {
WidgetsFlutterBinding.ensureInitialized();
SharedPreferences.getInstance().then((instance) {
_token = instance.getString("token");
final _loggedIn = _token != null && token != "";
runApp(MyApp(loggedIn: _loggedIn));
});
}
Then in your app add the parameters to switch:
class MyApp extends StatelessWidget {
final bool loggedIn;
MyApp({this.key, this.loggedIn});
#override
Widget build(BuildContext context) {
return MaterialApp(
home: loggedIn ? HomePage() : LoginPage(),
);
}
}
You can also use Navigator.pushReplacement() if you need to do it below MyApp(). Just posting it here for future generations.