I try to code like this
showModalBottomSheet(
context: context, // I got error here (Undefined name 'context'.dart(undefined_identifier))
builder: (context){
return Container(
);
);
I got error on context: context, error message is
Undefined name 'context'.dart(undefined_identifier)
This is how you call the showModalBottomSheet in a StatelessWidget
class TestStatelessWidget extends StatelessWidget{
#override
Widget build(BuildContext context) {
return RaisedButton(
child: Text('Press me'),
onPressed: ()=>showPress(context),
);
}
void showPress(BuildContext context){
showModalBottomSheet(context:context, builder: (context){
return Text('hello');
});
}
}
You are getting this error because you don't have access to context everywhere in a StatelessWidget class. All you need to do is pass context from build() if you are using this outside build() method else use it within build() method.
Solution 1. (Using inside build())
#override
Widget build(BuildContext context) {
return RaisedButton(
child: Text("Show sheet"),
onPressed: () {
showModalBottomSheet(context: context, builder: (context) => YourWidget());
},
);
}
Solution 2. (Using outside build())
#override
Widget build(BuildContext context) {
return RaisedButton(
child: Text("Show sheet"),
onPressed: () => _showSheet(context),
);
}
void _showSheet(BuildContext context) {
showModalBottomSheet(context: context, builder: (context) => YourWidget());
}
You did not close your showModalBottomSheet's builder correctly.
There is a } missing.
This would be the correct usage:
showModalBottomSheet(
context: context,
builder: (builder){
return Container();
}
);
Related
I have a preview widget that loads data after a user tap. This state (already tapped or not) should not be lost while scrolling (the preview is located in a list) or navigating through other screen.
The scrolling is solved by adding AutomaticKeepAliveClientMixin which saves the state when scrolling away.
Now i also need to wrap the preview widget (actually a more complex widget that contains the preview) with a RepaintBoundary, to be able to make a "screenshot" of this widget alone.
Before i wrap the widget with a RepaintBoundary, the state is saved both while scrolling and navigating to another screen.
After i add the RepaintBoundary the scrolling still works but for navigation the state is reset.
How can i wrap a Stateful widget that should hold its state with a RepaintBoundary?
Code is a simplified example of my implementation with the same problem.
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
MyApp({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
final title = 'Test';
return MaterialApp(
title: title,
home: Scaffold(
appBar: AppBar(
title: Text(title),
),
body: TestList(40),
),
);
}
}
class TestList extends StatefulWidget {
final int numberOfItems;
TestList(this.numberOfItems);
#override
_TestListState createState() => _TestListState();
}
class _TestListState extends State<TestList> {
#override
Widget build(BuildContext context) {
print('_TestListState build.');
return ListView.builder(
itemCount: widget.numberOfItems,
itemBuilder: (context, index) {
return RepaintBoundary(
key: GlobalKey(),
child: Preview()
);
},
);
}
}
class Preview extends StatefulWidget {
#override
_PreviewState createState() => _PreviewState();
}
class _PreviewState extends State<Preview> with AutomaticKeepAliveClientMixin {
bool loaded;
#override
void initState() {
super.initState();
print('_PreviewState initState.');
loaded = false;
}
#override
bool get wantKeepAlive => true;
#override
Widget build(BuildContext context) {
super.build(context);
print('_PreviewState build.');
if(loaded) {
return GestureDetector(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => NewScreen()),
);
},
child: ListTile(
title: Text('Loaded. Tap to navigate.'),
leading: Icon(Icons.visibility),
),
);
} else {
return GestureDetector(
onTap: () {
setState(() {
loaded = true;
});
},
child: ListTile(
title: Text('Tap to load.'),
),
);
}
}
}
class NewScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('New Screen')),
body: Center(
child: Text(
'Navigate back and see if loaded state is gone.',
style: TextStyle(fontSize: 14.0),
),
),
);
}
}
Take a look at RepaintBoundary.wrap, it assigns the RepaintBoundary widget a key based on its child or childIndex so state is maintained:
class _TestListState extends State<TestList> {
#override
Widget build(BuildContext context) {
print('_TestListState build.');
return ListView.builder(
itemCount: widget.numberOfItems,
itemBuilder: (context, index) {
return RepaintBoundary.wrap(
Preview(),
index,
);
},
);
}
}
https://api.flutter.dev/flutter/widgets/RepaintBoundary/RepaintBoundary.wrap.html
EDIT: As per the below comments, it looks like this solution would break the screenshot ability so you'd have to store the list of children widgets in your state like so:
class _TestListState extends State<TestList> {
List<Widget> _children;
#override
void initState() {
super.initState();
_children = List.generate(
widget.numberOfItems,
(_) => RepaintBoundary(
key: GlobalKey(),
child: Preview(),
));
}
#override
Widget build(BuildContext context) {
print('_TestListState build.');
return ListView(children: _children);
}
}
I have two screens in my app.
Screen A runs a computationally expensive operation while opened, and properly disposes by cancelling animations/subscriptions to the database when dispose() is called to prevent memory leaks.
From Screen A, you can open another screen (Screen B).
When I use Navigator.pushNamed, Screen A remains in memory, and dispose() is not called, even though Screen B is now shown.
Is there a way to force disposal of Screen A when it is not in view?
Example code where first route is never disposed:
import 'package:flutter/material.dart';
void main() {
runApp(MaterialApp(
title: 'Navigation Basics',
home: FirstRoute(),
));
}
class FirstRoute extends StatefulWidget {
#override
_FirstRouteState createState() => _FirstRouteState();
}
class _FirstRouteState extends State<FirstRoute> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('First Route'),
),
body: RaisedButton(
child: Text('Open route'),
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
},
),
);
}
#override
void dispose() {
// Never called
print("Disposing first route");
super.dispose();
}
}
class SecondRoute extends StatefulWidget {
#override
_SecondRouteState createState() => _SecondRouteState();
}
class _SecondRouteState extends State<SecondRoute> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
body: RaisedButton(
onPressed: () {
Navigator.pop(context);
},
child: Text('Go back!'),
),
);
}
#override
void dispose() {
print("Disposing second route");
super.dispose();
}
}
I know it's a bit late but I think you should override the deactivate method. Since we are changing the page we are not actually destroying it, that's why the dispose isn't being called.
If you'd like more information this page lists the lifecycle of the stateful widgets.
From the link:
'deactivate()' is called when State is removed from the tree, but it might be
reinserted before the current frame change is finished. This method exists basically
because State objects can be moved from one point in a tree to another.
call Navigator.pushReplacement when routing between first and second screen.
import 'package:flutter/material.dart';
void main() {
runApp(MaterialApp(
title: 'Navigation Basics',
home: FirstRoute(),
));
}
class FirstRoute extends StatefulWidget {
#override
_FirstRouteState createState() => _FirstRouteState();
}
class _FirstRouteState extends State<FirstRoute> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('First Route'),
),
body: RaisedButton(
child: Text('Open route'),
onPressed: () {
Navigator.pushReplacement(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
},
),
);
}
#override
void dispose() {
// Never called
print("Disposing first route");
super.dispose();
}
}
class SecondRoute extends StatefulWidget {
#override
_SecondRouteState createState() => _SecondRouteState();
}
class _SecondRouteState extends State<SecondRoute> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
body: RaisedButton(
onPressed: () {
Navigator.pushReplacement(
context,
MaterialPageRoute(builder: (context) => FirstRoute()),
);
},
child: Text('Go back!'),
),
);
}
#override
void dispose() {
print("Disposing second route");
super.dispose();
}
}
Try this
In flutter new versions deactivate won't be called when you push a new widget on top of another widget. Also there is an open issue related to this topic on flutter github: https://github.com/flutter/flutter/issues/50147
The best way to handle this issue is to add RouteObserver<PageRoute> to your material app and override didPushNext and didPushNext functions.
There is a very helpful medium article related to this topic which you can find here: https://medium.com/koahealth/how-to-track-screen-transitions-in-flutter-with-routeobserver-733984a90dea
As Article said create your own RouteAwareWidget, you can add these two call backs to the fields of the widget:
didPopNext
didPushNext
class RouteAwareWidget extends StatefulWidget {
final Widget child;
final VoidCallback? didPopNext;
final VoidCallback? didPushNext;
const RouteAwareWidget({
Key? key,
required this.child,
this.didPopNext,
this.didPushNext,
}) : super(key: key);
#override
State<RouteAwareWidget> createState() => RouteAwareWidgetState();
}
class RouteAwareWidgetState extends State<RouteAwareWidget> with RouteAware {
#override
void didChangeDependencies() {
super.didChangeDependencies();
routeObserver.subscribe(this, ModalRoute.of(context) as PageRoute);
}
#override
void dispose() {
routeObserver.unsubscribe(this);
super.dispose();
}
#override
void didPush() {}
#override
void didPopNext() {
dPrint('didPopNext');
widget.didPopNext == null ? null : widget.didPopNext!();
super.didPopNext();
}
#override
void didPushNext() {
dPrint('didPushNext');
widget.didPushNext == null ? null : widget.didPushNext!();
super.didPushNext();
}
#override
Widget build(BuildContext context) => widget.child;
}
Create a global RouteObserver<PageRoute> and add it to your material app:
final RouteObserver<PageRoute> routeObserver = RouteObserver<PageRoute>();
MaterialApp(
navigatorObservers: [routeObserver],
debugShowCheckedModeBanner: false,
routes: _routes,
)
then in your routs you should wrap your routes with RouteAwareWidget and add custom function you want:
final _routes = {
HomePage.routeName: (context) => RouteAwareWidget(
child: const HomePage(),
didPushNext: () => sl<CameraBloc>().add(Dispose()),
didPopNext: () => sl<CameraBloc>().add(Init()),
),
MyQuestions.routeName: (context) => const RouteAwareWidget(
child: MyQuestions(),
),
};
didPushNext will be called when you push a widget on top of HomePage and didPopNext will be called when you pop the last widget above HomePage.
With Navigator.pushReplacement(), if using MaterialPageRoute, then setting
maintainState:false
will ensure that dispose() is called.
A light weight solution for a single route case is using a callback function triggered from the SecondRoute.
Trigger the callback from the WidgetsBinding.instance.addPostFrameCallback() within the initState() on the SecondRoute
More information on WidgetsBinding and when they run can be found here: Flutter: SchedulerBinding vs WidgetsBinding.
WidgetsBinding & SchedulerBinding will be printed only once as we called it initState(), but it will be called when build method finished it’s rendering.
import 'package:flutter/material.dart';
class FirstRoute extends StatefulWidget {
const FirstRoute({super.key});
#override
State<FirstRoute> createState() => _FirstRouteState();
}
class _FirstRouteState extends State<FirstRoute> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text('Screen A')),
body: Center(
child: TextButton(
child: const Text('Go to Screen B'),
onPressed: () async {
await Navigator.of(context).push(
MaterialPageRoute(
builder: (BuildContext context) => SecondRoute(_callbackFn),
),
);
_secondRouteDone();
},
),
),
);
}
_callbackFn() {
print("Widget B Loaded, Free up memory, dispose things, etc.");
}
_secondRouteDone() {
print("SecondRoute Popped, Reinstate controllers, etc.");
}
}
class SecondRoute extends StatefulWidget {
final Function() notifyIsMountedFn;
const SecondRoute(this.notifyIsMountedFn, {super.key});
#override
State<SecondRoute> createState() => _SecondRouteState();
}
class _SecondRouteState extends State<SecondRoute> {
#override
void initState() {
super.initState();
// Notify FirstRoute after paint
WidgetsBinding.instance.addPostFrameCallback((_) {
widget.notifyIsMountedFn();
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text('Screen B')),
);
}
}
Not only to call 'deactivate()' but also to use 'Navigator.pushReplacement()' for page moving is necessary. Not working if you are using 'Navigator.push()'.
I'm trying to work with hero widget .. every thing working fine.. my problem the tag for hero should be unique .. for the main scaffold i can make it unique by using the id from my api .. but i can't pass this id to the second Scaffold ... it become undefined .. how i can defined it ,,,
My Code is
import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:json/add.dart';
Future<List> getData() async {
String url = 'http://192.168.0.57:4000/api/contacts';
http.Response response = await http.get(url);
return json.decode(response.body);
}
List data;
void main() async {
data = await (getData());
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
routes: <String, WidgetBuilder>{
'/Add': (BuildContext context) => new Add(),
},
home: HomePage(),
);
}
}
class HomePage extends StatefulWidget {
#override
State<StatefulWidget> createState() {
// TODO: implement createState
return HomePageState();
}
}
class HomePageState extends State<HomePage> {
#override
Widget build(BuildContext context) {
// TODO: implement build
return new MaterialApp(
title: "Test",
home: new Scaffold(
appBar: AppBar(
centerTitle: true,
title: new Text("Chat"),
),
body: new Center(
child: new ListView.builder(
itemCount: data.length,
itemBuilder: (BuildContext context, int position) {
return new ListTile(
title: new Text('${data[position]['name']}'),
subtitle: new Text('${data[position]['email']}'),
leading: new InkWell(
onTap: () {
Navigator.push(context,
MaterialPageRoute(builder: (BuildContext context) {
return HeroPage();
}));
},
child: Hero(
tag: "${data[position]['id']}",
child: new CircleAvatar(
child: new Text("${data[position]['name'][0]}"),
),
),
),
onTap: () {},
);
}),
),
),
);
}
}
class HeroPage extends StatefulWidget {
#override
State<StatefulWidget> createState() {
// TODO: implement createState
return HeroPageState();
}
}
class HeroPageState extends State<HeroPage> {
#override
Widget build(BuildContext context) {
// TODO: implement build
return new Scaffold(
appBar: AppBar(),
body: Hero(
tag: "${data[position]['id']}",
child: new Container(
color: Colors.blueAccent,
),
),
);
}
}
You can Pass the Position(Int) with help of Class Constructors.
class HeroPage extends StatefulWidget {
final int position;
final List data;
HeroPage({this.position,this.data});
#override
State<StatefulWidget> createState() {
// TODO: implement createState
return HeroPageState();
}
}
class HeroPageState extends State<HeroPage> {
#override
Widget build(BuildContext context) {
// TODO: implement build
return new Scaffold(
appBar: AppBar(),
body: Hero(
tag: "${widget.data[widget.position]['id']}",
child: new Container(
color: Colors.blueAccent,
),
),
);
}
}
Call the page like in your InkWell onTap::
Navigator.push(context,
MaterialPageRoute(builder: (BuildContext context) {
return HeroPage(position: position,data: data);
In the another page, try to wrap you hero in a ListView.builder, but the trick is only to set 1 in the itemCount param, with this, you can manipulate to show only one and get the correct tag
Currently I get the BuildContext from the build method in HomeScreen, and then I have to pass it down to _gridSliver then down to _storeCard.
How can I write the code so that I don't need to pass the context down?
Maybe I can create a new private StatelessWidget called _StoreCard that will have its own build method and thus its own BuildContext?
class HomeScreen extends StatelessWidget {
HomeScreen({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
return StoreConnector<AppState, List<MyStore.Store>>(
converter: (Store<AppState> store) => store.state.home.stores,
builder: (BuildContext context, List<MyStore.Store> stores) =>
CustomScrollView(slivers: <Widget>[_gridSliver(stores, context)]));
}
Widget _gridSliver(stores, context) {
return SliverGrid(
delegate: SliverChildListDelegate(List<Widget>.from(stores.map(_storeCard, context))));
}
Widget _storeCard(MyStore.Store store, BuildContext context) {
return InkWell(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(builder: (_) => StoreScreen(storeId: store.id)),
);
},
child: Container(child: Text(store.name))
);
}
}
Another instance of this problem is I navigate on a child function.
#override
Widget build(BuildContext context) {
return Column(
children: [
WhiteButton(text: "Login with Facebook", onPressed: _loginWithFacebook),
WhiteButton(text: "Login with Google", onPressed: _loginWithGoogle),
])
)
}
_loginWithFacebook(context) async {
...
var user = User.fromFacebook(result.accessToken.token, json.decode(graphResponse.body));
await _login(user, context);
}
}
_loginWithGoogle(context) async {
...
GoogleSignInAccount googleUser = await _googleSignIn.signIn();
await _login(User.fromGoogle(googleUser), context);
}
_login(user, context) async {
var fetchedUser = await MeService.getUser(user);
if (fetchedUser != null) {
loginSuccess(fetchedUser);
Navigator.popUntil(context, ModalRoute.withName(MainRoutes.root));
} else {
Navigator.push(
context,
MaterialPageRoute(builder: (_) => RegisterScreen(user: user)),
);
}
}
To get a new BuildContext, you have two main solutions:
Extract part of the subtree into a new widget, typically StatelessWidget. And then use it's BuildContext from the build method
Use Builder widget, which is basically a reusable widget made to obtain a BuildContext:
Example:
#override
Widget build(BuildContext context) {
return Builder(
builder: (context) {
// do something with this new context
},
);
}
You have to use a Bloc pattern that uses an Inherited Widget, but still you'll have to pass context, but in a more straight forward way. I recommend using this app by Stephen Grider, to figure out how the whole thing works. He explains in his tutorial how to put the whole thing together but I can't link you to that because that would be advertising.
The idea is, you first create a file Bloc.dart that is going to contain your logic, then you create what is called a Provider, in a Provider.dart.
Provider.dart:
class Provider extends InheritedWidget {
final bloc = Bloc();
Provider({Key key, Widget child}) : super(key: key, child: child);
bool updateShouldNotify(_) => true;
static Bloc of(BuildContext context) {
return (context.inheritFromWidgetOfExactType(Provider) as Provider).bloc;
}
}
In your file that contains the Material App, you wrap the material App with the provider:
Widget build(BuildContext context) {
return Provider(
child: MaterialApp(
And then you use the provider in every other class down the three of widgets.
class HomeScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
final bloc = Provider.of(context); // this is where you insert the provider
return StoreConnector<AppState, List<MyStore.Store>>(
converter: (Store<AppState> store) => store.state.home.stores,
builder: (BuildContext context, List<MyStore.Store> stores) =>
CustomScrollView(slivers: <Widget>[_gridSliver(stores, context)]));
}
Widget _gridSliver(stores) {
final bloc = Provider.of(context);
return SliverGrid(
delegate: SliverChildListDelegate(List<Widget>.from(stores.map(_storeCard, context))));
}
Widget _storeCard(MyStore.Store store) {
final bloc = Provider.of(context);
return InkWell(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(builder: (_) => StoreScreen(storeId: store.id)),
);
},
child: Container(child: Text(store.name))
);
}
}
I'm a total noob with flutter and take everything with grain of salt, but this is what I would use. Hope it helps.
I'm having trouble trying to access an InheritedWidget after navigating to a new widget.
I have my top level widget like this
class App extends StatelessWidget{
build(context){
return MaterialApp(
title: 'Iniciar Sesion',
home: LoginBlocProvider(child: WelcomeScreen()),
);
}
}
Then WelcomeScreen has a button to navigate to LoginScreen
class WelcomeScreen extends StatelessWidget {
#override Widget build(BuildContext context){
return Scaffold(
body: Center(child: MyButton)
);
}
}
class MyButton extends StatelessWidget {
#override
Widget build(BuildContext context) {
return RaisedButton(
shape: StadiumBorder(),
child: Text('Ingresar', style: TextStyle(color: Colors.black)),
elevation: 5.0,
onPressed: () {
Navigator.of(context).push(MaterialPageRoute(
builder: (BuildContext context) =>LoginScreen()
));
}
);
}
}
Finally in LoginScreen I want to access the InheritedWidget
class LoginScreen extends StatefulWidget {
#override
_LoginScreenState createState() => _LoginScreenState();
}
class _LoginScreenState extends State<LoginScreen> {
LoginBloc bloc;
#override void didChangeDependencies() {
bloc = LoginBlocProvider.of(context);
super.didChangeDependencies();
}
#override Widget build(BuildContext context){
return Scaffold(
body:
Stack(
fit: StackFit.expand,
children: <Widget>[
Positioned(
top: 0.0,
child: Image.asset('assets/images/img.jpg',
fit: BoxFit.none,
),
),
_buildLogin(),
],
),
);
}
}
Edited: Here it's the LoginBlocProvider
class LoginBlocProvider extends InheritedWidget {
final bloc;
LoginBlocProvider({Key key, Widget child})
: bloc = LoginBloc(),
super(key:key, child:child);
#override
bool updateShouldNotify(InheritedWidget oldWidget) => true;
static LoginBloc of(BuildContext context) {
return (context.inheritFromWidgetOfExactType(LoginBlocProvider) as LoginBlocProvider).bloc;
}
}
But, when I run the .of method of the InheritedWidget I get this error
I/flutter (27725): The following NoSuchMethodError was thrown building Builder:
I/flutter (27725): The getter 'bloc' was called on null.
I/flutter (27725): Receiver: null
I/flutter (27725): Tried calling: bloc
I have the impression that it all has to do with the context in the Navigator.push builder method.
Because if I use the LoginScreen widget without the Navigator.push, I can use the InheritedWidget perfectly fine
The error is happening because the context passed to the LoginBlocProvider.of() method is not finding the instance.
Any thoughts on this?
In the code you've provided, LoginScreen is not a descendant of LoginBlocProvider which is why it can't find the ancestor widget. Your code wraps the WelcomeScreen route in LoginBlocProvider, but not the whole navigator. The solution is to wrap your MaterialApp in LoginBlocProvider and then you will have access to it everywhere in your app.
class App extends StatelessWidget {
#override
Widget build(context) {
return LoginBlocProvider(
child: MaterialApp(
title: 'Iniciar Sesion',
home: WelcomeScreen(),
),
);
}
}
InheritedWidget should wrap the full MatrialApp widget (root widget)