Null check operator used on a null value Carousel Flutter - flutter

Question

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;
}
}

Answer 1

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.

Answer 2

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;

Answer 3

Just upgrade to ^3.0.0 Check here https://pub.dev/packages/carousel_slider

Answer 4

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.

Answer 5

I solved the similar problem as follows. You can take advantage of the Boolean variable. I hope, help you.
child: !loading ? HomeCarousel(homeManager) : Center(child:ProgressIndicator()),
or
child: isLoading ? HomeCarousel(homeManager) : SplashScreen(),
class SplashScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Text('Loading...')
),
);
}
}