I am refactor app to use scoped_model but have issue. State not seem to be pass correct between widget.
I am start with add ScopedModel to top of widget tree on startup.:
#override
Widget build(BuildContext context) {
UserModel().initialiseValues();
return ScopedModel<UserModel>(
model: UserModel(),
child: MaterialApp(
home: new Page(),
),
);
}
This call .initialiseValues(); so the model read from SharedPreferences and store in variables:
class UserModel extends Model {
String _name;
String get name => _name;
void initialiseValues() async {
SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
_name = sharedPrefs.getString('name');
print(‘_name from sharedPrefs is $_name');
print(‘name from sharedPrefs is $name');
notifyListeners();
}
}
Both print statement return correct name.
But when I try call using ScopedModelDescendant in another page name return null:
class PageFive extends StatelessWidget {
#override
Widget build(BuildContext context) {
return ScopedModelDescendant<UserModel>(
builder: (context, child, model) =>
Text('${model.name}'),
);
}
}
Text('${model.name}'), return null
Anyone know why name return null?
I have look hard for solve but no idea why.
There seems to be two problems:
1.- You are calling .initialiseValues() in a static way when the method is not static. And then you are creating a new diferent UserModel inside the ScopedModel.
2.- You are calling an async function inside the first build() method but you are not certain when it is going to finish and possibly, the UserModel is not fully initialized when building the tree.
You should maybe have a boolean variable (or check the .name for null) and set it to true when initialized.
In the build method, if that variable is false you could return a CircularProgressIndicator and when true just return your widget.
#override
Widget build(BuildContext context) {
var userModel = UserModel()..initialiseValues();
return ScopedModel<UserModel>(
model: userModel,
child: MaterialApp(
home: new Page(),
),
);
}
class PageFive extends StatelessWidget {
#override
Widget build(BuildContext context) {
return ScopedModelDescendant<UserModel>(
builder: (context, child, model) {
if (model.name == null)
return CircularProgressIndicator();
else
return Text('${model.name}');
});
}
}
Related
i want to be able to call an empty variable from a class, assign a value to it and make it persistent, anything aside provider e.t.c would be help, i don't want to overhaul the entire app again to do some bloc, provider e.t.c
NB: all screens are stateful widgets
i have tried creating a class with an empty string and passing a value to it from another screen, but this doesn't seem to work
import 'package:cloud_firestore/cloud_firestore.dart';
import 'dart:async';
import 'package:firebase_auth/firebase_auth.dart';
class MethodA {
// id(user, context){
// var name =user.email;
// }
String identity;
MethodA({this.iD});
bool isLoggedIn() {
if (FirebaseAuth.instance.currentUser() != null) {
return true;
} else {
return false;
}
}
Future<void> addUserA( userinfo) async {
//this.iD=id;
Firestore.instance
.collection('user')
.document('furtherinfo').collection(identity).document('Personal Info')
.setData(userdoc)
.catchError((e) {
print(e);
});
}
each time i pass the argument to i.e foo='bar';
and i import that class in another screen, i.e screen 9, foo is automatically set to null, but i would want foo to be bar
I would suggest that you use the Provider since it is the easiest way for me to manage state throughout the app. Flutter starts with one component on top of the widget tree so i would place my provider here.
Example
void main() {runApp(MyApp());}
class MyApp extends StatelessWidget {
MyApp();
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
StreamProvider<FirebaseUser>.value(
stream: FirebaseAuth.instance.onAuthStateChanged, // Provider to manage user throughout the app.
),
],
child: MaterialApp(
title: 'My App',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primaryColor: Colors.green,
primarySwatch: Colors.green,
accentColor: Colors.yellow,
),
home: MainPage(),
),
);
}
}
Then in your class you can do the following
class MethodAService with ChangeNotifier {
String _identity = null;
FirebaseUser _user = null;
// constructor with the (new changes )
MethodAService(FirebaseUser user){
this._user = user;
}
get identity => _identity ;
setIdentity(String identity) {
_identity = identity ;
notifyListeners(); // required to notify the widgets of your change
}
}
Then when you want to use it anywhere in your app just do the following in the build method
#override
Widget build(BuildContext context) {
final user = Provider.of<FirebaseUser>(context); // to get the current user
final methodA = Provider.of<MethodAService>(context); // get your service with identity
// now you can set the string using
methodA.setIdentity('new identity');
// or just use it like this
if(methodA.identity.isNotEmpty()){
print(methodA.identity);
}else{
print('Identity is empty');
}
return ChangeNotifierProvider<MethodAService>(
builder: (context) => MethodAService(user), // Your provider to manage your object, sending the Firebase user in
child: loggedIn ? HomePage() : LoginPage(), );
}
References
Provider Package
Fireship 185 Provider
Great Youtube video explaining the code
Update for comment
For getting the user uid you can just do user.uid
Changed code above to fit the
I'm not sure put the whole app in a StreamProvider is the best choice. That means the app will be rebuilt on each stream value.
To make a Widget available on all screens, you need a TransitionBuilder in your MaterialApp.
To avoid the external dependency you can also use an InheritedWidget
signed_user.dart
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
class SignedUser extends InheritedWidget {
final FirebaseUser user;
SignedUser({#required this.user, #required Widget child})
: super(child: child);
#override
bool updateShouldNotify(SignedUser oldWidget) => true;
static SignedUser of(BuildContext context) =>
context.inheritFromWidgetOfExactType(SignedUser);
}
my_transition_builder.dart
class MyTransitionBuilder extends StatefulWidget {
final Widget child;
const MyTransitionBuilder({Key key, this.child}) : super(key: key);
#override
_MyTransitionBuilderState createState() => _MyTransitionBuilderState();
}
class _MyTransitionBuilderState extends State<MyTransitionBuilder> {
StreamBuilder<FirebaseUser> _builder;
#override
void initState() {
super.initState();
_builder = StreamBuilder<FirebaseUser>(
stream: FirebaseAuth.instance.onAuthStateChanged,
builder: (context, snapshot) {
return SignedUser(
child: widget.child,
user: snapshot.data,
);
});
}
#override
Widget build(BuildContext context) {
return _builder;
}
}
main.dart
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
// this will make your inherited widget available on all screens of your app
builder: (context, child) {
return MyTransitionBuilder(child: child);
},
routes: {
'/editAccount': (context) => new EditAccountPage(),
},
theme: ThemeData(
primarySwatch: Colors.green,
),
home: MyHomePage(),
);
}
}
usage in edit_account_page.dart
#override
Widget build(BuildContext context) {
var user = SignedUser.of(context).user;
return Scaffold(
body: FutureBuilder<DocumentSnapshot>(
future: Firestore.instance.document('users/${user.uid}').get(),
I've been trying without success to load different pages according to my Shared Preference settings.
Based on several posts found in stackoverflow, i end up with the following solution:
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:testing/screens/login.dart';
import 'package:testing/screens/home.dart';
void main() => runApp(MyApp());
class MyApp extends StatefulWidget {
#override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
Widget page = Login();
Future getSharedPrefs() async {
String user = Preferences.local.getString('user');
if (user != null) {
print(user);
this.page = Home();
}
}
#override
void initState() {
super.initState();
this.getSharedPrefs();
}
#override
Widget build(BuildContext context) {
return MaterialApp(home: this.page);
}
}
class Preferences {
static SharedPreferences local;
/// Initializes the Shared Preferences and sets the info towards a global variable
static Future init() async {
local = await SharedPreferences.getInstance();
}
}
The variable user is not null because the print(user) returns a value as expected, but the login screen is always being opened.
Your problem is that your build method returns before your getSharedPrefs future is complete. The getSharedPrefs returns instantly as soon as it's called because it's async and you're treating it as a "Fire and Forget" by not awaiting. Seeing that you can't await in your initState function that makes sense.
This is where you want to use the FutureBuilder widget. Create a Future that returns a boolean (or enum if you want more states) and use a future builder as your home child to return the correct widget.
Create your future
Future<bool> showLoginPage() async {
var sharedPreferences = await SharedPreferences.getInstance();
// sharedPreferences.setString('user', 'hasuser');
String user = sharedPreferences.getString('user');
return user == null;
}
When user is null this will return true. Use this future in a Future builder to listen to the value changes and respond accordingly.
#override
Widget build(BuildContext context) {
return MaterialApp(home: FutureBuilder<bool>(
future: showLoginPage(),
builder: (buildContext, snapshot) {
if(snapshot.hasData) {
if(snapshot.data){
// Return your login here
return Container(color: Colors.blue);
}
// Return your home here
return Container(color: Colors.red);
} else {
// Return loading screen while reading preferences
return Center(child: CircularProgressIndicator());
}
},
));
}
I ran this code and it works fine. You should see a blue screen when login is required and a red screen when there's a user present. Uncomment the line in showLoginPage to test.
There is a much pretty way of doing this.
Assuming that you have some routes and a boolean SharedPreference key called initialized.
You need to use the WidgetsFlutterBinding.ensureInitialized() function before calling runApp() method.
void main() async {
var mapp;
var routes = <String, WidgetBuilder>{
'/initialize': (BuildContext context) => Initialize(),
'/register': (BuildContext context) => Register(),
'/home': (BuildContext context) => Home(),
};
print("Initializing.");
WidgetsFlutterBinding.ensureInitialized();
await SharedPreferencesClass.restore("initialized").then((value) {
if (value) {
mapp = MaterialApp(
debugShowCheckedModeBanner: false,
title: 'AppName',
theme: ThemeData(
primarySwatch: Colors.blue,
),
routes: routes,
home: Home(),
);
} else {
mapp = MaterialApp(
debugShowCheckedModeBanner: false,
title: 'AppName',
theme: ThemeData(
primarySwatch: Colors.blue,
),
routes: routes,
home: Initialize(),
);
}
});
print("Done.");
runApp(mapp);
}
The SharedPreference Class Code :
class SharedPreferencesClass {
static Future restore(String key) async {
final SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
return (sharedPrefs.get(key) ?? false);
}
static save(String key, dynamic value) async {
final SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
if (value is bool) {
sharedPrefs.setBool(key, value);
} else if (value is String) {
sharedPrefs.setString(key, value);
} else if (value is int) {
sharedPrefs.setInt(key, value);
} else if (value is double) {
sharedPrefs.setDouble(key, value);
} else if (value is List<String>) {
sharedPrefs.setStringList(key, value);
}
}
}
Look at this code - widget to fetch data and display on list:
class _MyEventsFragmentState extends State <MyEventsFragment>{
var events;
#override
initState(){
super.initState();
events = fetchEvents(true);
}
#override
Widget build(BuildContext context) {
return new Center(
child: FutureBuilder<EventsResponse>(
future: events,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.hasError) {
helpers.logout(context, Strings.msg_session_expired);
return CircularProgressIndicator();
}
return new Container(color: Colors.white,
child: new ListControl().build(snapshot));
}
return CircularProgressIndicator();
},
)
);
}
}
fetchEvent method has parameter to indicate which events I need to fetch. If set to true, - my events, if set to false - all events returned. Above code loads my events and fetchEvents is called inside initState override to avoid unnecesary data reloading.
To fetch all events I defined another class:
class EventsFragment extends StatefulWidget {
#override
_EventsFragmentState createState() => new _EventsFragmentState();
}
class _EventsFragmentState extends State <EventsFragment>{
var events;
#override
initState(){
super.initState();
events = fetchEvents(false);
}
#override
Widget build(BuildContext context) {
return new Center(
child: FutureBuilder<EventsResponse>(
future: events,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.hasError) {
helpers.logout(context, Strings.msg_session_expired);
return CircularProgressIndicator();
}
return new Container(color: Colors.white,
child: new ListControl().build(snapshot));
}
return CircularProgressIndicator();
},
)
);
}
}
But this is very dumb solution, because code is almost the same. So I tried to pass boolean value to indicate which events to load, something like that:
#override
initState(){
super.initState();
events = fetchEvents(isMyEvents);
}
isMyEvents should be got from EventsFragment constructor. However, it won't be accesible inside initState. Ho to pass it properly? I could access it inside build override, but not inside initState. How to pass it properly and make sure it will be refreshed every time widget instance is created?
[edit]
So this how I solved my problem (it seems to be fine):
class EventsFragment extends StatefulWidget {
const EventsFragment({Key key, this.isMyEvent}) : super(key: key);
final bool isMyEvent;
#override
_EventsFragmentState createState() => new _EventsFragmentState();
}
class _EventsFragmentState extends State <EventsFragment>{
var events;
#override
initState(){
super.initState();
events = fetchEvents(widget.isMyEvent);
}
#override
void didUpdateWidget(EventsFragment oldWidget) {
if(oldWidget.isMyEvent != widget.isMyEvent)
events = fetchEvents(widget.isMyEvent);
super.didUpdateWidget(oldWidget);
}
#override
Widget build(BuildContext context) {
return new Center(
child: FutureBuilder<EventsResponse>(
future: events,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.hasError) {
helpers.logout(context, Strings.msg_session_expired);
return CircularProgressIndicator();
}
return new Container(color: Colors.white,
child: new ListControl().build(snapshot));
}
return CircularProgressIndicator();
},
)
);
}
}
Pass such parameter to the StatefulWidget subclass, and use that field instead
class Foo extends StatefulWidget {
const Foo({Key key, this.isMyEvent}) : super(key: key);
final bool isMyEvent;
#override
_FooState createState() => _FooState();
}
class _FooState extends State<Foo> {
#override
void initState() {
super.initState();
print(widget.isMyEvent);
}
#override
Widget build(BuildContext context) {
return Container(
);
}
}
If I were using a StatefulWidget, then I would be listening to a Stream for example inside the initState method. Where would I do the equivalent in a StatelessWidget (like to use Bloc with streams for state management)? I could do it in the build method but since these are repetitively I wondered if there is a more efficient way than checking for existent listeners like below. I know that this is a redundant and useless example but it's just to show the problem.
import "package:rxdart/rxdart.dart";
import 'package:flutter/material.dart';
final counter = BehaviorSubject<int>();
final notifier = ValueNotifier<int>(0);
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
if (!counter.hasListener)
counter.listen((value) => notifier.value += value);
return MaterialApp(
home: Scaffold(
body: Center(
child:FlatButton(
onPressed: () => counter.add(1),
child: ValueListenableBuilder(
valueListenable: notifier,
builder: (context, value, child) => Text(
value.toString()
),
),
)
),
)
);
}
}
There is no clean way to have a StatelessWidget listen to a Listenable/Stream.
You will always need a StatefulWidget.
On the other hand, you can use composition to write that StatefulWidget just once, and be done with it.
Common examples for that pattern are widgets such as ValueListenableBuilder, StreamBuilder, or AnimatedBuilder. But it is possible to do the same thing, for listening too.
You'd use it this way:
class Foo extends StatelessWidget {
Foo({Key key, this.counter}): super(key: key);
final ValueListenable<int> counter;
#override
Widget build(BuildContext context) {
return ValueListenableListener(
valueListenable: counter,
onChange: (value) {
// TODO: do something
},
child: Something(),
);
}
}
Where ValueListenableListener is implemented this way:
class ValueListenableListener<T> extends StatefulWidget {
const ValueListenableListener(
{Key key, this.valueListenable, this.onChange, this.child})
: super(key: key);
final ValueListenable<T> valueListenable;
final ValueChanged<T> onChange;
final Widget child;
#override
_ValueListenableListenerState createState() =>
_ValueListenableListenerState();
}
class _ValueListenableListenerState extends State<ValueListenableListener> {
#override
void initState() {
super.initState();
widget.valueListenable?.addListener(_listener);
_listener();
}
#override
void didUpdateWidget(ValueListenableListener oldWidget) {
super.didUpdateWidget(oldWidget);
if (oldWidget.valueListenable != widget.valueListenable) {
oldWidget.valueListenable?.removeListener(_listener);
widget.valueListenable?.addListener(_listener);
_listener();
}
}
#override
void dispose() {
widget.valueListenable?.removeListener(_listener);
super.dispose();
}
void _listener() {
widget.onChange?.call(widget.valueListenable.value);
}
#override
Widget build(BuildContext context) {
return widget.child;
}
}
You shouldn't. Not handling variables that might have their values modified is the very purpose of a Stateless widget:
A stateless widget never changes.
UPDATE:
I think this is a problem of understanding Flutter's state management concepts. This new recommended way by the Flutter team should clear some confusions.
You could do something like this:
class ExampleWidget extends StatelessWidget {
bool _initialized = false;
#override
Widget build(BuildContext context) {
if (!_initialized) {
_initialized = true;
// Add listeners here only once
}
return Container();
}
}
But you shouldn't! In fact, your IDE will give you a warning, because this is not the way to go with Stateless widget as it is marked as #immutable. If you need to use lifecycle methods (like initState()) you should make it a Stateful widget. There's no big deal.
This is achievable with flutter_bloc package. The code to be run in initstate can be added inside BlocListener on whatever state you want.
BlocProvider(
create: (BuildContext context) =>
CategoryBlock()..add(LoadCategories()),
child: BlocListener<CategoryBlock, CategoryStates>(
listener: (context, state) {
//Example to add a listener for listview
if (state is LoadCategoriesSuccess) {
itemPositionsListener.itemPositions.addListener(() {
print(itemPositionsListener.itemPositions.value);
});
}
}
You could have your streams being instantiated in a StatefulWidget and then passed down to your StatelessWidgets as an option, so the parent widget would only have a role of controlling the lifecycle of the stream while the child would be using the stream to update the view.
Regarding the earlier answer:
There's no problem in using StreamBuilders inside your StatelessWidgets since the StreamBuilder itself is a a Widget that extends from StatefulWidget and will take care of it's own state and dispose correctly on its own.
Quite often I only want to draw a Widget based on a condition.
For example, I may be creating a component that displays a FadeIn.image but the image: may not be set in the CMS. In this case I want to ignore drawing the FadeIn.image and just return an empty container.
for context, I had done,
child: (someValue == null) ? new Container() : new LabelComponent(label: myStringLabel)
But this broke hot reload and I needed to replace with,
child: _createLabelComponent(myStringLabel),
Widget _createLabelComponent(String label)
{
if(label == null) {
return new Container();
} else {
return new LabelComponent(label: label)
}
}
Is the below safe to work and will not break hot reload? It seems to work at the moment but before I replace all my conditions with this Widget, I'd like some more feedback.
class ConditionalWidget extends StatefulWidget {
final bool condition;
final Widget conditionalWidget;
ConditionalWidget(this.condition, this.conditionalWidget, {Key key});
#override
State createState() => new ConditionalWidgetState();
}
class ConditionalWidgetState extends State<ConditionalWidget> {
ConditionalWidgetState();
#override
void initState()
{
super.initState();
}
#override
Widget build(BuildContext context)
{
if(widget.condition) {
return widget.conditionalWidget;
} else {
return new Container();
}
}
}
Nothing magic here, child is a property of a Container class:
it is safe to use whatever expression returns a widget for child property, obviously also conditional expressions
condition ? expr1 : expr2.
If hot reload in broken check for other causes.
For example your code that break hot reload:
child: (someValue == null) ? new Container() : new LabelComponent(label: myStringLabel)
uses someValue and myStringLabel, whereas in _createLabelComponent there is only a label variable.
class StatmentExample extends StatelessWidget {
Widget build(BuildContext context) {
return Text((() {
if(true){
return "tis true";}
return "anything but true";
})());
}
}
wrap your statements in a function
(() {
// your code here
}())