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Good Morning, I'm trying to put a Carousel on the home page looking for Firebase data, but for some reason, the first time I load the application it appears the message below:
════════ Exception caught by widgets library ═════════════════════════════════════ ══════════════════
The following _CastError was thrown building DotsIndicator (animation: PageController # 734f9 (one client, offset 0.0), dirty, state: _AnimatedState # 636ca):
Null check operator used on a null value
and the screen looks like this:
After giving a hot reload the error continues to appear, but the image is loaded successfully, any tips of what I can do?
HomeManager:
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:provantagens_app/models/section.dart';
class HomeManager extends ChangeNotifier{
HomeManager({this.images}){
_loadSections();
images = images ?? [];
}
void addSection(Section section){
_editingSections.add(section);
notifyListeners();
}
final List<dynamic> _sections = [];
List<String> images;
List<dynamic> newImages;
List<dynamic> _editingSections = [];
bool editing = false;
bool loading = false;
int index, totalItems;
final Firestore firestore = Firestore.instance;
Future<void> _loadSections() async{
loading = true;
firestore.collection('home').snapshots().listen((snapshot){
_sections.clear();
for(final DocumentSnapshot document in snapshot.documents){
_sections.add( Section.fromDocument(document));
images = List<String>.from(document.data['images'] as List<dynamic>);
}
});
loading = false;
notifyListeners();
}
List<dynamic> get sections {
if(editing)
return _editingSections;
else
return _sections;
}
void enterEditing({Section section}){
editing = true;
_editingSections = _sections.map((s) => s.clone()).toList();
defineIndex(section: section);
notifyListeners();
}
void saveEditing() async{
bool valid = true;
for(final section in _editingSections){
if(!section.valid()) valid = false;
}
if(!valid) return;
loading = true;
notifyListeners();
for(final section in _editingSections){
await section.save();
}
for(final section in List.from(_sections)){
if(!_editingSections.any((s) => s.id == section.id)){
await section.delete();
}
}
loading = false;
editing = false;
notifyListeners();
}
void discardEditing(){
editing = false;
notifyListeners();
}
void removeSection(Section section){
_editingSections.remove(section);
notifyListeners();
}
void onMoveUp(Section section){
int index = _editingSections.indexOf(section);
if(index != 0) {
_editingSections.remove(section);
_editingSections.insert(index - 1, section);
index = _editingSections.indexOf(section);
}
notifyListeners();
}
HomeManager clone(){
return HomeManager(
images: List.from(images),
);
}
void onMoveDown(Section section){
index = _editingSections.indexOf(section);
totalItems = _editingSections.length;
if(index < totalItems - 1){
_editingSections.remove(section);
_editingSections.insert(index + 1, section);
index = _editingSections.indexOf(section);
}else{
}
notifyListeners();
}
void defineIndex({Section section}){
index = _editingSections.indexOf(section);
totalItems = _editingSections.length;
notifyListeners();
}
}
HomeScreen:
import 'package:carousel_pro/carousel_pro.dart';
import 'package:flutter/material.dart';
import 'package:provantagens_app/commom/custom_drawer.dart';
import 'package:provantagens_app/commom/custom_icons_icons.dart';
import 'package:provantagens_app/models/home_manager.dart';
import 'package:provantagens_app/models/section.dart';
import 'package:provantagens_app/screens/home/components/home_carousel.dart';
import 'package:provantagens_app/screens/home/components/menu_icon_tile.dart';
import 'package:provider/provider.dart';
import 'package:url_launcher/url_launcher.dart';
// ignore: must_be_immutable
class HomeScreen extends StatelessWidget {
HomeManager homeManager;
Section section;
List<Widget> get children => null;
String videoUrl = 'https://www.youtube.com/watch?v=VFnDo3JUzjs';
int index;
var _tapPosition;
@override
Widget build(BuildContext context) {
return Container(
decoration: BoxDecoration(
gradient: LinearGradient(colors: const [
Colors.white,
Colors.white,
], begin: Alignment.topCenter, end: Alignment.bottomCenter)),
child: Scaffold(
backgroundColor: Colors.transparent,
drawer: CustomDrawer(),
appBar: AppBar(
backgroundColor: Colors.transparent,
iconTheme: IconThemeData(color: Colors.black),
title: Text('Página inicial', style: TextStyle(color: Color.fromARGB(255, 30, 158, 8))),
centerTitle: true,
actions: <Widget>[
Divider(),
],
),
body: Consumer<HomeManager>(
builder: (_, homeManager, __){
return ListView(children: <Widget>[
AspectRatio(
aspectRatio: 1,
child:HomeCarousel(homeManager),
),
Column(
children: <Widget>[
Container(
height: 50,
),
Divider(
color: Colors.black,
),
Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: [
Padding(
padding: const EdgeInsets.only(left:12.0),
child: MenuIconTile(title: 'Parceiros', iconData: Icons.apartment, page: 1,),
),
Padding(
padding: const EdgeInsets.only(left:7.0),
child: MenuIconTile(title: 'Beneficios', iconData: Icons.card_giftcard, page: 2,),
),
Padding(
padding: const EdgeInsets.only(right:3.0),
child: MenuIconTile(title: 'Suporte', iconData: Icons.help_outline, page: 6,),
),
],
),
Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: [
MenuIconTile(iconData: Icons.assignment,
title: 'Dados pessoais',
page: 3)
,
MenuIconTile(iconData: Icons.credit_card_outlined,
title: 'Meu cartão',
page: 4)
,
MenuIconTile(iconData: Icons.account_balance_wallet_outlined,
title: 'Pagamento',
page: 5,)
,
],
),
Divider(
color: Colors.black,
),
Container(
height: 50,
),
Consumer<HomeManager>(
builder: (_, sec, __){
return RaisedButton(
child: Text('Teste'),
onPressed: (){
Navigator.of(context)
.pushReplacementNamed('/teste',
arguments: sec);
},
);
},
),
Text('Saiba onde usar o seu', style: TextStyle(color: Colors.black, fontSize: 20),),
Text('Cartão Pró Vantagens', style: TextStyle(color: Color.fromARGB(255, 30, 158, 8), fontSize: 30),),
AspectRatio(
aspectRatio: 1,
child: Image.network(
'https://static.wixstatic.com/media/d170e1_80b5f6510f5841c19046f1ed5bca71e4~mv2.png/v1/fill/w_745,h_595,al_c,q_90,usm_0.66_1.00_0.01/Arte_Cart%C3%83%C2%B5es.webp',
fit: BoxFit.fill,
),
),
Divider(),
Container(
height: 150,
child: Row(
children: [
AspectRatio(
aspectRatio: 1,
child: Image.network(
'https://static.wixstatic.com/media/d170e1_486dd638987b4ef48d12a4bafee20e80~mv2.png/v1/fill/w_684,h_547,al_c,q_90,usm_0.66_1.00_0.01/Arte_Cart%C3%83%C2%B5es_2.webp',
fit: BoxFit.fill,
),
),
Padding(
padding: const EdgeInsets.only(left:20.0),
child: RichText(
text: TextSpan(children: <TextSpan>[
TextSpan(
text: 'Adquira já o seu',
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
),
TextSpan(
text: '\n\CARTÃO PRÓ VANTAGENS',
style: TextStyle(
fontSize: 15.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 30, 158, 8)),
),
]),
),
),
],
),
),
Divider(),
tableBeneficios(),
Divider(),
Padding(
padding: const EdgeInsets.all(16.0),
child: Column(
children: [
Text(
'O cartão Pró-Vantagens é sediado na cidade de Hortolândia/SP e já está no mercado há mais de 3 anos. Somos um time de profissionais apaixonados por gestão de benefícios e empenhados em gerar o máximo de valor para os conveniados.'),
FlatButton(
onPressed: () {
launch(
'https://www.youtube.com/watch?v=VFnDo3JUzjs');
},
child: Text('SAIBA MAIS')),
],
),
),
Container(
color: Color.fromARGB(255, 105, 190, 90),
child: Column(
children: <Widget>[
Row(
children: [
Padding(
padding: const EdgeInsets.all(16),
child: Text(
'© 2020 todos os direitos reservados a Cartão Pró Vantagens.',
style: TextStyle(fontSize: 10),
),
)
],
),
Divider(),
Row(
children: [
Padding(
padding: const EdgeInsets.all(16),
child: Text(
'Rua Luís Camilo de Camargo, 175 -\n\Centro, Hortolândia (piso superior)',
style: TextStyle(fontSize: 10),
),
),
Padding(
padding: const EdgeInsets.only(left: 16),
child: IconButton(
icon: Icon(CustomIcons.facebook),
color: Colors.black,
onPressed: () {
launch(
'https://www.facebook.com/provantagens/');
},
),
),
Padding(
padding: const EdgeInsets.only(left: 16),
child: IconButton(
icon: Icon(CustomIcons.instagram),
color: Colors.black,
onPressed: () {
launch(
'https://www.instagram.com/cartaoprovantagens/');
},
),
),
],
),
],
),
)
],
),
]);
},
)
),
);
}
tableBeneficios() {
return Table(
defaultColumnWidth: FlexColumnWidth(120.0),
border: TableBorder(
horizontalInside: BorderSide(
color: Colors.black,
style: BorderStyle.solid,
width: 1.0,
),
verticalInside: BorderSide(
color: Colors.black,
style: BorderStyle.solid,
width: 1.0,
),
),
children: [
_criarTituloTable(",Plus, Premium"),
_criarLinhaTable("Seguro de vida\n\(Morte Acidental),X,X"),
_criarLinhaTable("Seguro de Vida\n\(Qualquer natureza),,X"),
_criarLinhaTable("Invalidez Total e Parcial,X,X"),
_criarLinhaTable("Assistência Residencial,X,X"),
_criarLinhaTable("Assistência Funeral,X,X"),
_criarLinhaTable("Assistência Pet,X,X"),
_criarLinhaTable("Assistência Natalidade,X,X"),
_criarLinhaTable("Assistência Eletroassist,X,X"),
_criarLinhaTable("Assistência Alimentação,X,X"),
_criarLinhaTable("Descontos em Parceiros,X,X"),
],
);
}
_criarLinhaTable(String listaNomes) {
return TableRow(
children: listaNomes.split(',').map((name) {
return Container(
alignment: Alignment.center,
child: RichText(
text: TextSpan(children: <TextSpan>[
TextSpan(
text: name != "X" ? '' : 'X',
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
),
TextSpan(
text: name != 'X' ? name : '',
style: TextStyle(
fontSize: 10.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 30, 158, 8)),
),
]),
),
padding: EdgeInsets.all(8.0),
);
}).toList(),
);
}
_criarTituloTable(String listaNomes) {
return TableRow(
children: listaNomes.split(',').map((name) {
return Container(
alignment: Alignment.center,
child: RichText(
text: TextSpan(children: <TextSpan>[
TextSpan(
text: name == "" ? '' : 'Plano ',
style: TextStyle(
fontSize: 15.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
),
TextSpan(
text: name,
style: TextStyle(
fontSize: 15.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 30, 158, 8)),
),
]),
),
padding: EdgeInsets.all(8.0),
);
}).toList(),
);
}
void _storePosition(TapDownDetails details) {
_tapPosition = details.globalPosition;
}
}
267
Use the fallback operator to set a default value for null values before using the variable. Here, "str" is null, and we set the fallback operator with fallback value in case of "str" is null. You need to do this before using it on the code.
When creating { question: 'How old are you?' , answer: null } try specify the precise type you want like <String, dynamic>{ question: 'How old are you?' , answer: null } .
Here, "str" is null, and we set the fallback operator with fallback value in case of "str" is null. You need to do this before using it on the code. You can use this method to handle Null values to escape the "Null check operator used on a null value" error in Flutter or Dart.
In this example, we are going to show you how to show you the cause and solution of the "Null check operator used on a null value" error in the Flutter App. This error occurs when you add (!) Null check operator on Null value. For example: The operator (!) is used on null value "str".
Null check operator on Null value. For example: The operator (!) is used on null value "str". To solve this issue, see the different examples below: Here, we check if the "str" String variable is null or not before getting the length. If you are using the nullable value on Widget, then do like below:
The issue might be related to the null safety that is getting integrated in dartlang. For now you can switch channels and use the stable channel: This is related to the sound null safety in dart. Try switching to the stable channel by flutter channel stable then upgrade by flutter upgrade
I forked the library to create a custom carousel for my company's project, and since we updated flutter to 2.x we had the same problem.
To fix this just update boolean expressions like
if(carouselState.pageController.position.minScrollExtent == null ||
carouselState.pageController.position.maxScrollExtent == null){ ... }
to
if(!carouselState.pageController.position.hasContentDimensions){ ... }
Here is flutter's github reference.
111
This worked for me
So I edited scrollposition.dart package
from line 133
@override
//double get minScrollExtent => _minScrollExtent!;
// double? _minScrollExtent;
double get minScrollExtent {
if (_minScrollExtent == null) {
_minScrollExtent = 0.0;
}
return double.parse(_minScrollExtent.toString());
}
double? _minScrollExtent;
@override
// double get maxScrollExtent => _maxScrollExtent!;
// double? _maxScrollExtent;
double get maxScrollExtent {
if (_maxScrollExtent == null) {
_maxScrollExtent = 0.0;
}
return double.parse(_maxScrollExtent.toString());
}
double? _maxScrollExtent;
Just upgrade to ^3.0.0 Check here https://pub.dev/packages/carousel_slider
2
I faced the same issue. This is how I solved it
class PlansPage extends StatefulWidget {
const PlansPage({Key? key}) : super(key: key);
@override
State<PlansPage> createState() => _PlansPageState();
}
class _PlansPageState extends State<PlansPage> {
int _currentPage = 1;
late CarouselController carouselController;
@override
void initState() {
super.initState();
carouselController = CarouselController();
}
}
Then put initialization the carouselController inside the initState method I was able to use the methods jumpToPage(_currentPage ) and animateToPage(_currentPage) etc.
I use animateToPage inside GestureDetector in onTap.
onTap: () {
setState(() {
_currentPage = pageIndex;
});
carouselController.animateToPage(_currentPage);
},
I apologize in advance if this is inappropriate.
1
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