I'm trying to access the information I've passed over from a previous class before the build method begins. But it's saying only static members can be accessed in initializers. I don't really want to use the static property, partially because I wouldn't know how to use it, but also because I think it seems unnecessary. In previous pages I've been able to access the data but only after the build method, does anyone know how I can access it before? Thanks all
class FirstPage extends StatefulWidget {
#override
_FirstPageState createState() => _FirstPageState();
}
class _FirstPageState extends State<FirstPage> {
List<MyProvider> myList;
#override
Widget build(BuildContext context) {
return Scaffold(
body: ListView.builder(
itemCount: myList.length,
itemBuilder: (context, index) {
String imgPath = myList[index].image;
String myTextPath = myList[index].name;
String locationNamePath = myList[index].location;
double distancePath = myList[index].distance;
String myName = '${myTextPath} ''${locationNamePath}';
return MyCard(
locationText: locationNamePath,
myText: myTextPath,
assetImage: Image.network(imgPath),
function: (){
Provider.of<Data>(context, listen: false).addLogo(Image.network(imgPath));
Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage(myName: myName,)));
},
);
}),
);
}
}
My next page accesses the data using a key but it seems not to be able to use it before the build method, and that's what I need to get around!
class SecondPage extends StatefulWidget {
final String myName;
const SecondPage({Key key, this.myName})
: super(key: key);
#override
_SecondPageState createState() => _SecondPageState();
}
class _SecondPageState extends State<SecondPage> with TickerProviderStateMixin {
final CollectionReference myItemsReference = Firestore.instance.collection('${widget.myName}');
// This is where the error is
#override
Widget build(BuildContext context) {
return Scaffold();
}
}
Use the initState method for anything related to initialization of State. See this for more on initState.
Example:
CollectionReference myItemsReference;
#override
void initState() {
myItemsReference = Firestore.instance.collection('${widget.myName}');
}
Related
I'm new to Riverpod and am trying to migrate an app over from Provider. If I had a TextField and wanted to set its value based on my Provider model, I would do this:
class MyWidget extends StatefulWidget{
const MyWidget({ Key? key }) : super(key: key);
#override
State<MyWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
var controller = TextEditingController();
#override
void didChangeDependencies() {
super.didChangeDependencies();
//Set the value here...
var model = Provider.of<Model>(context);
controller.text = model.name;
}
Widget build(BuildContext context) {
return TextField(controller: controller)
}
}
As I understand it, didChangeDependencies() would listen to changes from Provider.of<Model>(context) and update my controller accordingly.
I'm trying to pull off the same thing with Provider, but I can't ever get the TextField's value to show up.
class MyWidget extends ConsumerStatefulWidget {
const MyWidget({Key? key}) : super(key: key);
#override
ConsumerState<ConsumerStatefulWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends ConsumerState<MyWidget> {
var controller = TextEditingController();
#override
void didChangeDependencies() {
super.didChangeDependencies();
//Trying the same thing here...
final name = ref.watch(providerName);
controller.text = name;
}
Widget build(BuildContext context) {
final name = ref.watch(providerName);
return Column(
children: [
//This doesn't work:
TextField(controller: controller),
//I know my provider has the value, because this works fine:
Text(name),
]
}
}
How can I get my TextEditingController's text property to update?
From Riverpod official website
///1.Create a [StateNotifier] sub-class, StateNotifier is something where you can define functions that can change your state like in this state is of String type, you also can use objects (Classes instead of primitive types)
class Counter extends StateNotifier<String> {
Counter() : super('');
void changeText(String text){
state=text;
}
///2.Create a provider [StateNotifierProvider] with this you can use in your widget
final counterProvider = StateNotifierProvider<Counter, String>((ref) {
return Counter();
});
///3.Consume the Provider this is how we can attach state with our widget
class Home extends ConsumerWidget {
#override
Widget build(BuildContext context, WidgetRef ref) {
final text = ref.watch(counterProvider);
return Text('$text');
}
}
so here you can add you widget like button and onTap executes the code like
onTap()=>changeText(textController.text);
So your text [Text('$text');] will automatically change.
String inputText = controller.text;
I am still with my first bloc based app, adding features. While previously, I stored some of my page specific data with the bloc class, for the last feature, I now moved most variables into its repository. I already feared that the instance of calling the repository gets lost, afterwards, which now proved true.
Is there a proper, easy way to make the instance persistent?
I know of inherited widgets, however, I have not yet figured out how to implement this and my question around this unfortunately remained unanswered. It would be great, if someone could point me to some direction!
In general, my idea was to have the api dealing with local files and online data, the repository with frequently re-used data (session data, presented data etc) and helper variables within the bloc. So when the UI requests data, the bloc asks the repository which will either return a value stored in a variable or request a value from the api.
This is, how the strucuture basically looks like (hope I have not missed anything significant)
void main() async {
final UserRepository userRepository = UserRepository(); // <===== userRepository initialized
runApp(MyApp(userRepository: UserRepository()));
}
class MyApp extends StatelessWidget {
MyApp({Key key, this.userRepository}) : assert(userRepository != null), super(key: key);
final UserRepository userRepository;
#override
Widget build(BuildContext context) {
return BlocProvider<UserBloc>( <====== userBloc injection to top of widget tree
create: (_) => UserBloc(userRepository: userRepository)..add(AppStarted()),
child: App(),
);
}
}
// =================================================== APP WITH ROUTES
class App extends StatelessWidget {
App({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
return CupertinoApp(
routes: {
'/': (_) => HomePage(),
'feature 1': (_) => HomePage(),
},
);
}
}
// =================================================== LANDING PAGE WITH MAIN MENU
class HomePage extends StatefulWidget {
HomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
#override
Widget build(BuildContext context) {
SystemChrome.setPreferredOrientations([
DeviceOrientation.portraitUp,
]);
return CupertinoPageScaffold(
navigationBar: CupertinoNavigationBar(
middle: Text('MathUup'),
),
child: SafeArea(
child: CupertinoButton(
child: Text('Feature 1',
onPressed: () => Navigator.pushNamed(context, 'feature 1'),
),)));
}}
// =================================================== BLOC
class UserBloc extends Bloc<UserEvent, UserState> {
UserBloc({this.userRepository}) : super(AppInitial());
final UserRepository userRepository;
...
final user = await userRepository.getActiveUserData(userId);
final lastSessionData = await userRepository.getLastSession(userId);
...
}
// =================================================== REPOSITORY
class UserRepository {
UserRepository();
final UserApiClient achievementsApiClient = UserApiClient();
final SessionsApiClient sessionsApiClient = SessionsApiClient();
UserSession activeUserSession;
User activeUserData;
Future<String> getLastUserId() async {
final lastUserId = await sessionsApiClient.getLastUserId();
return lastUserId;
}
Future<UserSession> getActiveUser() async {
if (activeUserSession == null) {
activeUserSession = await sessionsApiClient.getLastUser();
}
return activeUserSession;
}
}
This line is creating and initializing your user repository:
final UserRepository userRepository = UserRepository(); // <===== userRepository initialized
However, this line is not passing that repository, it's creating a new repository, ignoring the one you just initialized:
runApp(MyApp(userRepository: UserRepository()));
I think you meant to use the variable you already have:
runApp(MyApp(userRepository: userRepository));
this is my code, i dont know how to pass this listOfTiles to my StatefulWidget, can u help me and describe how it works?
body: new ListView.builder(
itemBuilder: (BuildContext context, int index) {
return new StuffInTilesState(listOfTiles[index]);//i want to pass this
},
itemCount: listOfTiles.length,
),
),
);
}
}
class StuffInTiles extends StatefulWidget{
#override
StuffInTilesState createState() => StuffInTilesState();//i know i need to change this, but i dont know how
}
class StuffInTilesState extends State<StuffInTiles> {
final MyTile myTile;
StuffInTilesState(this.myTile);//this is constructor, shuld this also be changed?
final _controller = TextEditingController();
String name = "";
If u want to see my working code: https://pastebin.pl/view/c4dbc2af If u want to see my not working code: https://pastebin.pl/view/83f9cad0 (https://codeshare.io/GLLm66)
You need to use the widget class constructor and not the state class.
You can access the values in the state class with widget.YouProperty
class StuffInTiles extends StatefulWidget {
final MyTile myTile;
const StuffInTiles(this.myTile);
#override
_StuffInTilesState createState() => _StuffInTilesState();
}
class _StuffInTilesState extends State<StuffInTiles> {
#override
Widget build(BuildContext context) {
return Container(child:
Text(widget.myTile),);
}
}
Get variable data from a Stateful widget in another Stateful widget and they have no relation to one another (They are not children nor parents to each other)
I want to be able to access an array (posts) that is located in another file... You can see the comments in the code for more information
I have this stateful widget
import 'package:flutter/material.dart';
import 'package:saviortv/modules/fetchPosts.dart';
import 'package:saviortv/ui/BuildPost.dart';
class Home extends StatefulWidget {
#override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
#override
Widget build(BuildContext context) {
return ListView.builder(
itemCount: posts == null ? 0 : posts.length, // <== here posts is undefined because it doesn't exist as I want to get it from the other file (See below)
itemBuilder: (BuildContext context, int index) {
return buildPost(context, posts, index); //Building the posts list view
},
);
}
}
The other Stateful widget
class FetchPosts extends StatefulWidget {
FetchPosts({Key key, this.pageNumber = 1}) : super(key: key);
final int pageNumber;
#override
_FetchPostsState createState() => _FetchPostsState(pageNumber);
}
class _FetchPostsState extends State<FetchPosts> {
_FetchPostsState(this.pageNumber);
int pageNumber;
List<wp.Post> posts = []; //<== I want this to be useable in the other file;
Future<String> getPosts() async {
var res = await fetchPosts(pageNumber);
print(pageNumber);
setState(() {
posts = res;
});
return "Success!";
}
// Get _ when app loads;
#override
void initState() {
super.initState();
this.getPosts();
}
#override
Widget build(BuildContext context) {
return Container();
}
}
How can I achieve that?
I have 2 screens in my Flutter app: a list of records and a screen for creating and editing records.
If I pass an object to the second screen that means I am going to edit this and if I pass null it means that I am creating a new item. The editing screen is a Stateful widget and I am not sure how to use this approach https://flutter.io/cookbook/navigation/passing-data/ for my case.
class RecordPage extends StatefulWidget {
final Record recordObject;
RecordPage({Key key, #required this.recordObject}) : super(key: key);
#override
_RecordPageState createState() => new _RecordPageState();
}
class _RecordPageState extends State<RecordPage> {
#override
Widget build(BuildContext context) {
//.....
}
}
How can I access recordObject inside _RecordPageState?
To use recordObject in _RecordPageState, you have to just write widget.objectname like below
class _RecordPageState extends State<RecordPage> {
#override
Widget build(BuildContext context) {
.....
widget.recordObject
.....
}
}
Full Example
You don't need to pass parameters to State using it's constructor.
You can easily access these using widget.myField.
class MyRecord extends StatefulWidget {
final String recordName;
const MyRecord(this.recordName);
#override
MyRecordState createState() => MyRecordState();
}
class MyRecordState extends State<MyRecord> {
#override
Widget build(BuildContext context) {
return Text(widget.recordName); // Here you direct access using widget
}
}
Pass your data when you Navigate screen :
Navigator.of(context).push(MaterialPageRoute(builder: (context) => MyRecord("WonderWorld")));
class RecordPage extends StatefulWidget {
final Record recordObject;
RecordPage({Key key, #required this.recordObject}) : super(key: key);
#override
_RecordPageState createState() => new _RecordPageState(recordObject);
}
class _RecordPageState extends State<RecordPage> {
Record recordObject
_RecordPageState(this. recordObject); //constructor
#override
Widget build(BuildContext context) {. //closure has access
//.....
}
}
example as below:
class nhaphangle extends StatefulWidget {
final String username;
final List<String> dshangle;// = ["1","2"];
const nhaphangle({ Key key, #required this.username,#required this.dshangle }) : super(key: key);
#override
_nhaphangleState createState() => _nhaphangleState();
}
class _nhaphangleState extends State<nhaphangle> {
TextEditingController mspController = TextEditingController();
TextEditingController soluongController = TextEditingController();
final scrollDirection = Axis.vertical;
DateTime Ngaysx = DateTime.now();
ScrollController _scrollController = new ScrollController();
ApiService _apiService;
List<String> titles = [];
#override
void initState() {
super.initState();
_apiService = ApiService();
titles = widget.dshangle; //here var is call and set to
}
I have to Navigate back to any one of the screens in the list pages but when I did that my onTap function stops working and navigation stops.
class MyBar extends StatefulWidget {
MyBar({this.pageNumber});
final pageNumber;
static const String id = 'mybar_screen';
#override
_MyBarState createState() => _MyBarState();
}
class _MyBarState extends State<MyBar> {
final List pages = [
NotificationScreen(),
AppointmentScreen(),
RequestBloodScreen(),
ProfileScreen(),
];
#override
Widget build(BuildContext context) {
var _selectedItemIndex = widget.pageNumber;
return Scaffold(
bottomNavigationBar: BottomNavigationBar(
elevation: 0,
backgroundColor: Colors.white,
unselectedItemColor: Colors.grey.shade700,
selectedItemColor: Color(kAppColor),
selectedIconTheme: IconThemeData(color: Color(kAppColor)),
currentIndex: _selectedItemIndex,
type: BottomNavigationBarType.fixed,
onTap: (int index) {
setState(() {
_selectedItemIndex = index;
});
},
You should use a Pub/Sub mechanism.
I prefer to use Rx in many situations and languages. For Dart/Flutter this is the package: https://pub.dev/packages/rxdart
For example, you can use a BehaviorSubject to emit data from widget A, pass the stream to widget B which listens for changes and applies them inside the setState.
Widget A:
// initialize subject and put it into the Widget B
BehaviorSubject<LiveOutput> subject = BehaviorSubject();
late WidgetB widgetB = WidgetB(deviceOutput: subject);
// when you have to emit new data
subject.add(deviceOutput);
Widget B:
// add stream at class level
class WidgetB extends StatefulWidget {
final ValueStream<LiveOutput> deviceOutput;
const WidgetB({Key? key, required this.deviceOutput}) : super(key: key);
#override
State<WidgetB> createState() => _WidgetBState();
}
// listen for changes
#override
void initState() {
super.initState();
widget.deviceOutput.listen((event) {
print("new live output");
setState(() {
// do whatever you want
});
});
}
In my app, often instead of using stateful widgets, I use mainly ChangeNotifierProvider<T> in main.dart, some model class
class FooModel extends ChangeNotifier {
var _foo = false;
void changeFooState() {
_foo = true;
notifyListeners();
}
bool getFoo () => _foo;
}
and
var foo = context.read<FooModel>();
# or
var foo = context.watch<FooModel>();
in my stateless widgets. IMO this gives me more precise control over the rebuilding upon runtime state change, compared to stateful widgets.
The recipe can be found in the official docs, the concept is called "lifting state up".