I want to trigger a boolean variable 'runBackdropBlur' in the state class as per below code.
To do this I want to be able to call the method turnOnBackdropBlur() (from another widget), and this method in turn, when called will change this variable in it's state class by use of global key.
I have been following this tutorial, to achieve a simple state management solution for this case:
tutorial
However, I run into these two errors in flutter, i cannot fix...
"Named parameters must be enclosed in curly braces ('{' and '}')."
"The default value of an optional parameter must be constant."
class Backdrop extends StatefulWidget {
Backdrop(key : _myKey);
GlobalKey<_BackdropState> _myKey = GlobalKey<_BackdropState>();
void turnOnBackdropBlur() {
_myKey.currentState!.runBackdropBlur = true;
}
#override
_BackdropState createState() => _BackdropState();
}
class _BackdropState extends State<Backdrop> {
bool runBackdropBlur = false;
//etc
With some tricks you can do everything you want. You can give a pointer of a method to the owner widget as follows:
import 'dart:developer';
import 'package:flutter/cupertino.dart';
class Backdrop extends StatefulWidget {
final Map<String, Function> listener = new Map<String, Function>();
void setnBackdropBlurTrue() => listener.containsKey("BackdropBlurTrue")
? listener["BackdropBlurTrue"].call()
: log("BackdropBlurTrue key is null");
void setnBackdropBlurFalse() => listener.containsKey("BackdropBlurFalse")
? listener["BackdropBlurFalse"].call()
: log("BackdropBlurFalse key is null");
#override
_BackdropState createState() => _BackdropState();
}
class _BackdropState extends State<Backdrop> {
bool runBackdropBlur = false;
void setRunBackdropBlurTrue() => runBackdropBlur = true;
void setRunBackdropBlurFalse() => runBackdropBlur = false;
#override
Widget build(BuildContext context) {
return Container();
}
_BackdropState() {
widget.listener.putIfAbsent("BackdropBlurTrue", () => setRunBackdropBlurTrue);
widget.listener.putIfAbsent("BackdropBlurFalse", () => setRunBackdropBlurFalse);
}
}
Related
I need to expose a couple of functions of a Stateful Widget. Since these functions depend on the state of the widget, I created a variable to store the state.
However, I am getting a compile time warning:
This class (or a class that this class inherits from) is marked as '#immutable', but one or more of its instance fields aren't final.
My Code:
class ItemWidget extends StatefulWidget {
final Record record;
final Function additem;
final Function removeItem;
var state;
ItemWidget(this.record, this.additem, this.removeItem);
#override
_ItemWidgetState createState() {
return this.state = new _ItemWidgetState();
}
// These are public functions which I need to expose.
bool isValid() => state.validate();
void validate() => state.validate();
}
Is there a better way /correct way of achieving this?
Thanks.
You should write the function on state, and access it via GlobalKey.
import 'package:flutter/material.dart';
class ItemWidget extends StatefulWidget {
final Record record;
final Function additem;
final Function removeItem;
const ItemWidget(
Key? key,
this.record,
this.additem,
this.removeItem,
) : super(key: key);
#override
ItemWidgetState createState() => ItemWidgetState();
}
class ItemWidgetState extends State<ItemWidget> {
bool isValid() {
return true;
}
void validate() {}
#override
Widget build(BuildContext context) {
// TODO: implement build
throw UnimplementedError();
}
}
https://api.flutter.dev/flutter/widgets/GlobalKey-class.html
am following this Bloc's official example and I couldn't find a way how to access the state without that if statement.
Let's have the example below, I would like to display a specific text based on the initial value of showText, the only possible solution to access the state is via:
if(statement is ExampleInitial) {state.showText? return Text("yes") : return Text("no")}
But am finding this solution hard to implement when you have more values with initial values. Or am I doing this wrong?
////////// bloc
class ExampleBloc extends Bloc<ExampleEvent, ExampleState> {
ExampleBloc() : super(const ExampleInitial()) {
on<ExampleStarted>(_onExampleStarted);
}
void _onExampleStarted(ExampleStarted event, Emitter<ExampleState> emit) {
emit(const ExampleInitial());
}
}
////////// event
part of 'example_bloc.dart';
abstract class ExampleEvent extends Equatable {
const ExampleEvent();
}
class ExampleStarted extends ExampleEvent {
#override
List<Object> get props => [];
}
////////// state
part of 'example_bloc.dart';
abstract class ExampleState extends Equatable {
const ExampleState();
}
////////// state
class ExampleInitial extends ExampleState {
final bool showText = false;
const ExampleInitial();
#override
List<Object> get props => [showText];
}
// ui
class CreateExampleScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BlocBuilder<ExampleBloc, ExampleState>(
builder: (context, state) {
return state.showText ? Text("yes") :Text("no"); // can't access to state.showText
});
}
}
You can declare a variable inside Bloc Class which will be global and need to be set inside the 'bloc.dart' file like in the case of Provider Package. This variable does not need state to be checked before accessing it in UI. You can access this value from the Navigation tree using context.
////////// bloc
class ExampleBloc extends Bloc<ExampleEvent, ExampleState> {
ExampleBloc() : super(const ExampleInitial()) {
on<ExampleStarted>(_onExampleStarted);
}
bool showText = false;
void _onExampleStarted(ExampleStarted event, Emitter<ExampleState> emit) {
emit(const ExampleInitial());
}
}
// ui
class CreateExampleScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BlocProvider.of<ExampleBloc>(context).showText
? const Text('Yes')
: const Text('No');
}
}
There is another way in which you declare abstract State Class to always have the boolean value. So, whatever new class extends those State will have inherited boolean value from parent class. This concept is called inheritance in OOP.
////////// state
abstract class ExampleState extends Equatable {
const ExampleState();
final bool showText = false;
}
////////// state
class ExampleInitial extends ExampleState {
const ExampleInitial();
// You can also set ExampleInitial to accept showText and send it to its
// parent class using 'super' method in constructor,
// if parent class has constructor with 'showText' as boolean
#override
List<Object> get props => [];
}
// ui
class CreateExampleScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BlocBuilder<ExampleBloc, ExampleState>(builder: (context, state) {
return state.showText ? const Text("yes") : const Text("no");
});
}
}
A pragmatic usecase for different State Classes having different state variables is as follows:
Let's account for three states while fetching data from api
-if(state is DataLoadingState),
// there is no need for state
-if(state is DataLoadedState)
// state need to have a variable named weatherData containing temperatures, cities and so on.
-if(state is ErrorWhileLoadingState)
// state needs to have a reason for the error. For example: errorMsg: 'Internal Server Error'
So, you need to check the state before accessing its values.
I'm in the process of migrating over a large project to null safety and I'm coming across a strange error I'm not entirely sure how to fix.
"Error: Type argument 'T' doesn't conform to the bound 'Object' of the type variable 'T' on 'GetIt.call'."
class BaseView<T extends BaseProvider?> extends StatefulWidget {
final Widget Function(BuildContext context, T value, Widget? child)? builder;
final Function(T)? onModelReady;
BaseView({this.builder, this.onModelReady});
#override
_BaseViewState<T> createState() => _BaseViewState<T>();
}
class _BaseViewState<T extends BaseProvider?> extends State<BaseView<T?>> {
T model = locator<T>(); <---- This is throwing it
#override
void initState() {
if (widget.onModelReady != null) {
widget.onModelReady!(model);
}
super.initState();
}
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider<T?>(
create: (context) => model,
child: Consumer<T>(builder: widget.builder!),
);
}
}
I can't find much info on this error and so far any method I've tried hasn't worked out. Can anyone be of assistance?
I'm using Provider for state management and BaseView is what wraps all my other views during build; e.g.:
class EquipmentMainView extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BaseView<EquipmentProvider>(
onModelReady: (model) async {
model.getAllFunctions();
},..
Posting here for anyone else that might eventually run across this in the future, just changed the nullability of BaseProvider suggested by jamesdlin by changing
class BaseView<T extends BaseProvider?>
to
class BaseView<T extends BaseProvider>
I had similar issues when I upgraded to flutter 2.0 I made the generic methods in Generic class to explicitly extends Base class Object i.e
from:
import 'package:get_it/get_it.dart';
class PoultryBabaRegistry<T> {
static GetIt _getIt = GetIt.instance;
static void register<T>(T model) {
_getIt.registerSingleton<T extends Object >(model, signalsReady: true);
}
static void remove<T>(T model) {
_getIt.unregister<T extends Object>(instance:model);
}
static T getIt<T>() {
return _getIt.get<T>();
}
}
to:
class PoultryBabaRegistry<T extends Object> {
static GetIt _getIt = GetIt.instance;
static void register<T extends Object>(T model) {
_getIt.registerSingleton<T >(model, signalsReady: true);
}
static void remove<T extends Object>(T model) {
_getIt.unregister<T>(instance:model);
}
static T getIt<T extends Object>() {
return _getIt.get<T>();
}
}
In my project, I pass data from one widget to another using this code:
Navigator.push(
context,
MaterialPageRoute(
builder: (context) =>
TranslatorSignUpStep2(transModel: this._translatorModel),
),
);
Then I retrive it in the other widget by the code below:
class TranslatorSignUpStep2 extends StatefulWidget {
final TranslatorModel transModel;
TranslatorSignUpStep2({this.transModel});
#override
_TranslatorSignUpStep2State createState() => _TranslatorSignUpStep2State();
}
The problem is, in the TranslatorSignUpStep2 class I want to assign the passed-in transModel to another variable so I write this code
class _TranslatorSignUpStep2State extends State<TranslatorSignUpStep2> {
TranslatorModel _translatorModel = widget.transModel;
}
But it seems like the widget can't be used outside the build method so I get error saying
The instance member 'widget' can't be accessed in an initializer.. Anyone know how to get over this ?
you can access widget in initState function like this.
class _TranslatorSignUpStep2State extends State<TranslatorSignUpStep2> {
TranslatorModel _translatorModel ;
#override
void initState() {
_translatorModel = widget.transModel;
}
}
Just add the keyword late while initializing:
class TranslatorSignUpStep2 extends StatefulWidget {
final TranslatorModel transModel;
TranslatorSignUpStep2({this.transModel});
#override
_TranslatorSignUpStep2State createState() => _TranslatorSignUpStep2State();
}
class _TranslatorSignUpStep2State extends State<TranslatorSignUpStep2> {
late TranslatorModel _translatorModel = widget.transModel;
}
try this code :
TranslatorSignUpStep2 :
class TranslatorSignUpStep2 extends StatefulWidget {
final TranslatorModel transModel;
TranslatorSignUpStep2({this.transModel});
#override
_TranslatorSignUpStep2State createState() => _TranslatorSignUpStep2State(this.transModel);
}
TranslatorSignUpStep2 class :
class _TranslatorSignUpStep2State extends State<TranslatorSignUpStep2> {
_TranslatorSignUpStep2State(TranslatorModel _tempModel ){
this._translatorModel =_tempModel;
};
TranslatorModel _translatorModel ;
}
Add static keyword when innitializing
class OrderDetails extends StatefulWidget {
int selectedDays;
OrderDetails({
this.range,)};
#override
_OrderDetailsState createState() => _OrderDetailsState();
}
class _OrderDetailsState extends State<OrderDetails> {
String getRange;
#override
void initState() {
super.initState();
getRange = widget.range;
}
I'm still a beginner with streams and bloc pattern.
I would like to do following:
Trigger an event.
Based on the event get back a state with an object
Store this object as JSON in a database.
All examples are showing, how an object can be displayed in a widget with BlocBuilder. But I don't need to display the value, only get it and store it. I can't figure out how to get the value into a variable.
How can I do that? In the View class I'm dispatching the event, but now I need to know how to get the object in the state back without using BlocBuilder.
Here are the details:
Bloc
class SchoolBloc extends Bloc<SchoolEvent, SchoolState> {
final SchoolRepository _schoolRepository;
StreamSubscription _schoolSubscription;
SchoolBloc({#required SchoolRepository schoolRepository})
: assert(schoolRepository != null),
_schoolRepository = schoolRepository;
#override
SchoolState get initialState => SchoolsLoading();
#override
Stream<SchoolState> mapEventToState(SchoolEvent event) async* {
if (event is LoadSchool) {
yield* _mapLoadSchoolToState();
Stream<SchoolState> _mapLoadSchoolToState(LoadSchool event) async* {
_schoolSubscription?.cancel();
_schoolSubscription = _schoolRepository.school(event.id).listen(
(school) {
SchoolLoaded(school);
}
);
}
Event
#immutable
abstract class SchoolEvent extends Equatable {
SchoolEvent([List props = const []]) : super(props);
}
class LoadSchool extends SchoolEvent {
final String id;
LoadSchool(this.id) : super([id]);
#override
String toString() => 'LoadSchool';
}
State
#immutable
abstract class SchoolState extends Equatable {
SchoolState([List props = const []]) : super(props);
}
class SchoolLoaded extends SchoolState {
final School school;
SchoolLoaded([this.school]) : super([school]);
#override
String toString() => 'SchoolLoaded { school: $school}';
}
View
class CourseView extends StatefulWidget {
#override
State<StatefulWidget> createState() => _CourseViewState();
}
class _CourseViewState extends State<CourseView> {
#override
initState() {
super.initState();
print("this is my init text");
final _schoolBloc = BlocProvider.of<SchoolBloc>(context);
_schoolBloc.dispatch(LoadSchool("3kRHuyk20UggHwm4wrUI"));
// Here I want to get back the school object and save it to a db
}
Test that fails
For testing purposes I have done following:
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:teach_mob/core/blocs/school/school.dart';
class CourseView extends StatefulWidget {
#override
State<StatefulWidget> createState() => _CourseViewState();
}
class _CourseViewState extends State<CourseView> {
#override
void initState() {
super.initState();
BlocProvider.of<SchoolBloc>(context)
.dispatch(LoadSchool("3kRHuyk20UggHwm4wrUI"));
}
#override
Widget build(BuildContext context) {
return BlocListener<SchoolBloc, SchoolState>(
listener: (context, state) {
print("BlocListener is triggered");
},
child: Text("This is a test")
);
}
}
The LoadSchool event is triggered. The text in the child attribute of BlocListener is displayed, but the listener function that should print "BlocListener is triggered" is not executed.
Use BlocListener. It is meant to be used for those cases you mention.