Flutter 空值转盘颤振上使用的空检查运算符
早上好， 我试图在主页上放置一个转盘，查找Firebase数据，但由于某些原因，在我第一次加载应用程序时，它会显示以下消息：Flutter 空值转盘颤振上使用的空检查运算符,flutter,carousel,Flutter,Carousel,早上好， 我试图在主页上放置一个转盘，查找Firebase数据，但由于某些原因，在我第一次加载应用程序时，它会显示以下消息： ════════ Exception caught by widgets library ═════════════════════════════════════ ══════════════════ The following _CastError was thrown building DotsIndicator (animation: PageController
════════ 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
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();
}
}
import'包：cloud_firestore/cloud_firestore.dart'；
进口“包装：颤振/cupertino.dart”；
进口“包装：颤振/材料.省道”；
导入“package:provantagens_app/models/section.dart”；
类HomeManager扩展了ChangeNotifier{
家庭管理器（{this.images}）{
_加载段（）；
图像=图像？？？[]；
}
无效添加节（节）{
_编辑节。添加（节）；
notifyListeners（）；
}
最终清单_部分=[]；
列出图像；
列出新图像；
列表_editingSections=[]；
布尔编辑=假；
布尔加载=假；
整数索引，总计项；
最终Firestore Firestore=Firestore.instance；
Future\u loadSections（）异步{
加载=真；
firestore.collection（'home'）.snapshots（）.listen（（快照）{
_节。清除（）；
用于（最终文档snapshot.documents中的snapshot文档）{
_节.添加（节.来自文件（文件））；
images=List.from（document.data['images']作为列表）；
}
});
加载=假；
notifyListeners（）；
}
列出获取部分{
如果（编辑）
返回编辑部分；
其他的
返回部分；
}
无效输入编辑（{Section}）{
编辑=真；
_editingSections=_sections.map（（s）=>s.clone（））.toList（）；
定义索引（章节：章节）；
notifyListeners（）；
}
void saveEditing（）异步{
bool valid=true；
用于（编辑部分中的最后一部分）{
如果（！section.valid（））valid=false；
}
如果（！有效）返回；
加载=真；
notifyListeners（）；
用于（编辑部分中的最后一部分）{
等待节。保存（）；
}
用于（列表中的最后一节。从（_节））{
如果（！\u编辑节.any（（s）=>s.id==section.id））{
等待节。删除（）；
}
}
加载=假；
编辑=假；
notifyListeners（）；
}
无效编辑（）{
编辑=假；
notifyListeners（）；
}
无效清除（截面）{
_编辑节。删除（节）；
notifyListeners（）；
}
移动时无效（部分）{
int index=_editingSections.indexOf（section）；
如果（索引！=0）{
_编辑节。删除（节）；
_编辑章节。插入（索引-1，章节）；
索引=_editingSections.indexOf（section）；
}
notifyListeners（）；
}
HomeManager克隆（）{
返回家庭管理器(
图像：列表。从（图像），
);
}
移动时无效（截面）{
索引=_editingSections.indexOf（section）；
totalItems=_editingSections.length；
如果（索引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;
}
}
import'包：carousel_pro/carousel_pro.dart'；
进口“包装：颤振/材料.省道”；
导入“package:provantagens_app/commom/custom_drawer.dart”；
导入“package:provantagens_app/commom/custom_icons_icons.dart”；
导入“package:provantagens_app/models/home_manager.dart”；
导入“package:provantagens_app/models/section.dart”；
导入“包：provantagens_应用程序/屏幕/主页/组件/主页旋转木马.dart”；
导入“包：provantagens_应用程序/屏幕/主页/组件/菜单图标_tile.dart”；
导入“包：provider/provider.dart”；
导入“package:url_launcher/url_launcher.dart”；
//忽略：必须是不可变的
类主屏幕扩展无状态小部件{
家庭经理家庭经理；
部分；
List get children=>null；
字符串videoUrl=https://www.youtube.com/watch?v=VFnDo3JUzjs';
整数指数；
变量位置；
@凌驾
小部件构建（构建上下文）{
返回容器(
装饰：盒子装饰(
渐变：线性渐变（颜色：常量）[
颜色，白色，
颜色，白色，
]，开始：Alignment.topCenter，结束：Alignment.bottomCenter），
孩子：脚手架(
背景颜色：颜色。透明，
抽屉：CustomDrawer（），
appBar:appBar(
背景颜色：颜色。透明，
iconTheme:IconThemeData（颜色：Colors.black），
标题：文本（'Página inicial'，样式：TextStyle（颜色：color.fromARGB（255,30,158,8）），
标题：对，
行动：[
分隔符（），
],
),
主体：消费者(
建筑商：（uu，房屋经理，uuu）{
返回列表视图（子项：[
AspectRatio(
方面：1，
子女：家庭旋转木马（家庭经理），
),
纵队(
儿童：[
容器(
身高：50，
),
分隔器(
颜色：颜色，黑色，
),
划船(
mainAxisAlignment:mainAxisAlignment.spaceAround，
儿童：[
填充物(
填充：仅限常量边集（左：12.0），
子项：MenuIconTile（标题：“Parceiros”，iconda:Icons.plant，第1页，），
),
填充物(
填充：仅限常量边集（左：7.0），
子项：MenuIconTile（标题：“受益人”，iconda:Icons.card_giftcard，第2页，），
),
if(carouselState.pageController.position.minScrollExtent == null ||
carouselState.pageController.position.maxScrollExtent == null){ ... }
if(!carouselState.pageController.position.hasContentDimensions){ ... }
child: !loading ? HomeCarousel(homeManager) : Center(child:ProgressIndicator()),
child: isLoading ? HomeCarousel(homeManager) : SplashScreen(),
class SplashScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Text('Loading...')
),
);
}
}
@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;