Null check operator used on a null value Carousel Flutter
8,679
Solution 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.
Solution 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;
Solution 3
Just upgrade to ^3.0.0 Check here https://pub.dev/packages/carousel_slider
Author by
Admin
Updated on December 25, 2022Comments
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Admin over 1 year
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 valueand 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; } }