Develop Reference

How to show list of images in grid view builder if list is not empty

i have a list which contains list of images, i want to show these in my grid view builder if list if not empty other wise i just want to show static + symbol in my grid view builder.
it is my list
var otherPersonOfferList = <Inventory>[].obs;
and this is my grid view builder which i have extracted as a widget and using it in my screen
import 'package:bartermade/models/Get_Inventory.dart';
import 'package:bartermade/models/inventory.dart';
import 'package:bartermade/widgets/inventoryTile.dart';
import 'package:cached_network_image/cached_network_image.dart';
import 'package:flutter/material.dart';
import 'package:get/get.dart';
import '../controllers/inventoryController.dart';
class OfferGrid extends StatefulWidget {
OfferGrid(
{Key? key,
required this.list,
required this.modelSheetHeading,
required this.gestureState})
: super(key: key);
String modelSheetHeading;
List<Inventory> list;
bool gestureState;
#override
State<OfferGrid> createState() => _OfferGridState();
}
class _OfferGridState extends State<OfferGrid> {
InventoryController inventoryController = Get.find();
bool isDeleting = false;
#override
Widget build(BuildContext context) {
if (widget.gestureState == true
? (inventoryController.otherPersonOfferList == [] ||
inventoryController.otherPersonOfferList.length == 0 ||
inventoryController.otherPersonOfferList.isEmpty)
: (inventoryController.myOfferList == [] ||
inventoryController.myOfferList.length == 0 ||
inventoryController.myOfferList.isEmpty)) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: GestureDetector(
onTap: () {
showModalBottomSheet(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(20)),
context: context,
builder: (context) {
return InventoryTile(
modelSheetHeading: widget.modelSheetHeading,
list: widget.gestureState == true
? inventoryController.traderInventoryList
: inventoryController.myInventoryList1,
inventoryController: inventoryController,
gestureState: widget.gestureState);
});
},
child: Container(
height: 90,
width: 90,
decoration: BoxDecoration(border: Border.all(color: Colors.black)),
child: Icon(
Icons.add,
size: 35,
),
),
),
);
} else {
return GridView.builder(
shrinkWrap: true,
physics: NeverScrollableScrollPhysics(),
itemCount: widget.list.length + 1,
gridDelegate:
SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3),
itemBuilder: (context, index) {
if (index == widget.list.length) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: GestureDetector(
onTap: () {
showModalBottomSheet(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(20)),
context: context,
builder: (context) {
return InventoryTile(
modelSheetHeading: widget.modelSheetHeading,
list: widget.gestureState == true
? inventoryController.traderInventoryList
: inventoryController.myInventoryList1,
inventoryController: inventoryController,
gestureState: widget.gestureState);
});
},
child: Container(
height: 30,
width: 30,
decoration:
BoxDecoration(border: Border.all(color: Colors.black)),
child: Icon(
Icons.add,
size: 35,
),
),
),
);
} else {
return Stack(
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: GestureDetector(
onLongPress: () {
setState(() {
isDeleting = true;
});
},
onTap : (){
setState(() {
isDeleting = false;
});
},
child: CachedNetworkImage(
fit: BoxFit.cover,
height: 100,
width: 200,
imageUrl: // "https://asia-exstatic-vivofs.vivo.com/PSee2l50xoirPK7y/1642733614422/0ae79529ef33f2b3eb7602f89c1472b3.jpg"
"${widget.list[index].url}",
placeholder: (context, url) => Center(
child: CircularProgressIndicator(
color: Colors.grey,
),
),
errorWidget: (context, url, error) => Icon(Icons.error),
),
),
),
isDeleting == true
? Positioned(
right: 0,
top: 0,
child: CircleAvatar(
backgroundColor: Colors.red,
radius: 10,
child: Icon(
Icons.remove,
size: 14,
),
),
)
: SizedBox()
],
);
}
});
}
}
}
and this is my screen where is just want to check if my list is non empty then fill my grid view with images otherwise just show + sign in grid view
import 'package:bartermade/controllers/inventoryController.dart';
import 'package:bartermade/models/Get_Inventory.dart';
import 'package:bartermade/models/inventory.dart';
import 'package:bartermade/screens/chat/chatScreen.dart';
import 'package:bartermade/utils/app_colors.dart';
import 'package:bartermade/widgets/snackBar.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:get/get.dart';
import '../../../../services/inventoryService.dart';
import '../../../../widgets/offerGrid.dart';
class OfferTradeScreen extends StatefulWidget {
String postUserId;
String postUserName;
OfferTradeScreen({
Key? key,
required this.postUserId,
required this.postUserName,
}) : super(key: key);
#override
State<OfferTradeScreen> createState() => _OfferTradeScreenState();
}
class _OfferTradeScreenState extends State<OfferTradeScreen> {
// TradeController tradeController = Get.put(TradeController());
InventoryController inventoryController = Get.put(InventoryController());
// GiftStorageService giftStorageService = GiftStorageService();
// GiftController giftController = Get.put(GiftController());
// ProfileController profileController = Get.put(ProfileController());
// TradeStorageService tradeStorageService = TradeStorageService();
// TradingService tradingService = TradingService();
// PreferenceService preferenceService = PreferenceService();
late List<Inventory> otherPersonList;
late List<Inventory> myList;
#override
void initState() {
super.initState();
inventoryController.getOtherUserInventory(widget.postUserId);
otherPersonList = inventoryController.otherPersonOfferList;
myList = inventoryController.myOfferList;
}
otherPersonlistener() {
inventoryController.otherPersonOfferList.listen((p0) {
if (this.mounted) {
setState(() {
otherPersonList = p0;
});
}
});
}
mylistener() {
inventoryController.myOfferList.listen((p0) {
if (this.mounted) {
setState(() {
myList = p0;
});
}
});
}
int draggableIndex = 0;
#override
Widget build(BuildContext context) {
print("-------building------");
otherPersonlistener();
mylistener();
SystemChrome.setPreferredOrientations([
DeviceOrientation.portraitUp,
DeviceOrientation.portraitDown,
]);
return Scaffold(
appBar: AppBar(
titleSpacing: 0,
leading: GestureDetector(
onTap: () {
inventoryController.myOfferList.clear();
inventoryController.otherPersonOfferList.clear();
Get.back();
},
child: Icon(Icons.arrow_back)),
title: Text(
"Offer",
style: TextStyle(color: Colors.white),
),
actions: [
Padding(
padding: const EdgeInsets.only(right: 15),
child: GestureDetector(
onTap: () {
Get.to(() => ChatScreen(
currentUserId: widget.postUserId,
recieverId: inventoryController.userId.toString()));
},
child: Icon(Icons.message)),
)
],
),
body: Padding(
padding: const EdgeInsets.symmetric(horizontal: 20),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Expanded(
flex: 10,
child: Container(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Padding(
padding: const EdgeInsets.only(top: 20),
child: Text(
"${widget.postUserName} Inventory",
style: TextStyle(
color: Colors.black,
fontSize: 20,
fontWeight: FontWeight.w400),
),
),
OfferGrid(
gestureState: true,
list: otherPersonList,
modelSheetHeading: "${widget.postUserName}",
)
],
),
),
),
Expanded(
flex: 1,
child: Divider(
thickness: 2,
color: Colors.black,
height: 3,
),
),
Expanded(
flex: 10,
child: Container(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
"My Inventory",
style: TextStyle(
color: Colors.black,
fontSize: 20,
fontWeight: FontWeight.w400),
),
OfferGrid(
gestureState: false,
list: myList,
modelSheetHeading: "My Inventory",
)
],
),
),
),
Center(child: Obx(() {
return inventoryController.makingOffer.value == true
? CircularProgressIndicator(
color: AppColors.pinkAppBar,
)
: ElevatedButton(
onPressed: () {
if (inventoryController.otherPersonOfferList.isEmpty &&
inventoryController.myOfferList.isEmpty) {
showSnackBar(
"Please add both inventories to make offer",
context);
} else {
inventoryController.postOffer(
widget.postUserId, context);
}
},
style: ElevatedButton.styleFrom(
padding: EdgeInsets.symmetric(
vertical: 10, horizontal: 50)),
child: Text("Send Offer"));
}))
],
),
),
);
}
#override
void dispose() {
SystemChrome.setPreferredOrientations([
DeviceOrientation.landscapeRight,
DeviceOrientation.landscapeLeft,
DeviceOrientation.portraitUp,
DeviceOrientation.portraitDown,
]);
super.dispose();
}
}

User following code :
GridView.builder(
shrinkWrap: true,
itemCount: data.length,
gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 3,
crossAxisSpacing: 17,
mainAxisSpacing: 17,
),
itemBuilder: (
context,
index,
) {
return Obx(
() => InkWell(
onTap: () {
},
child: ClipRRect(
child: Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(20),
border: Border.all(
color: ColorConfig.colorDarkBlue, width: 2),
image: DecorationImage(
image: AssetImage(ImagePath.unselectedContainer), ///imageURL
fit: BoxFit.fill,
)),
child: Center(
child: Text(data[index].heading,
textAlign: TextAlign.center,
style: TextStyle(
fontSize: ThemeConstants.textThemeFontSize18,
fontWeight: FontWeight.w700,
color: ColorConfig.colorDarkBlue)),
),
height: 150,
),
),
),
);
},
),

Error is "The getter 'length' was called on null. Receiver: null Tried calling: length"

I am trying to develop a flutter app. This app is like a dating app. After writing all the code, everything is working fine as I expected But on the home screen, I got an exception, where I know where the exception and what it means, but i do not have any clue how i could solve the problem. I hope some of you guys could help me.
This is the code where the error is thrown:
import 'package:buis_talk/blocs/swipe/swipe_bloc.dart';
import 'package:buis_talk/widgets/widgets.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:buis_talk/models/models.dart';
class HomeScreen extends StatelessWidget {
static const String routeName = '/home';
// const HomeScreen({Key? key}) : super(key: key);
static Route route() {
return MaterialPageRoute(
settings: const RouteSettings(name: routeName),
builder: (context) => HomeScreen(),
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: const CustomAppBar(
title: 'Home',
),
body: BlocBuilder<SwipeBloc, SwipeState>(
builder: (context, state) {
var userCount = state.users.length;
return Column(
children: [
InkWell(
onDoubleTap: () {
Navigator.pushNamed(context, '/users',
arguments: state.users[0]
);
},
child: Draggable<User>(
data: state.users[0],
child: UserCard(user: state.users[0]),
feedback: UserCard(user: state.users[0]),
childWhenDragging: (userCount > 1) ?
UserCard(user: state.users[1]): Container(),
onDragEnd: (drag) {
if (drag.velocity.pixelsPerSecond.dx < 0) {
context.read<SwipeBloc>()
.add(SwipeLeft(user: state.users[0]));
print('Swiped left');
} else {
context.read<SwipeBloc>()
.add(SwipeRight(user: state.users[0]));
print('Swiped right');
}
},
),
),
Padding(
padding: const EdgeInsets.symmetric(
vertical: 8.0,
horizontal: 60,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
InkWell(
onTap: () {
context.read<SwipeBloc>()
.add(SwipeLeft(user: state.users[0]));
print('Swiped left');
},
child: ChoiceButton(
width: 60,
height: 60,
size: 25,
hasGradient: false,
color: Theme.of(context).colorScheme.secondary,
icon: Icons.clear_rounded,
),
),
InkWell(
onTap: () {
context.read<SwipeBloc>()
.add(SwipeRight(user: state.users[0]));
print('Swiped right');
},
child: const ChoiceButton(
width: 80,
height: 80,
size: 30,
hasGradient: true,
color: Colors.white,
icon: Icons.coffee,
),
),
ChoiceButton(
width: 60,
height: 60,
size: 25,
hasGradient: false,
color: Theme.of(context).primaryColor,
icon: Icons.watch_later,
),
],
),
),
],
);
}
),
);
}
}
And the error message is:
The getter 'length' was called on null.
Receiver: null
Tried calling: length
The relevant error-causing widget was:
BlocBuilder<SwipeBloc, SwipeState>
If I remove length from var usercount = state.users.length; => var usercount = state.users; then it gives me error is:
The method '[]' was called on null.
Receiver: null
Tried calling: [](0)
The relevant error-causing widget was:
BlocBuilder<SwipeBloc, SwipeState>

Do this,
var usercount = (state.users ?? []).length;
and its good to have checks, before doing this state.users[0]
check if the list has values like
if(state.users.isNotEmpty){
state.users[0];
}

How to pass method into another class in flutter

I tried to create a task app using flutter, So I created a text field in DialogBox and my aim is when I add some text into the text field and when I clicked the OK button, I need to show that text in the list. but I have no idea how to call a method in another class, I've added my two classes.
ListTask Class
import 'package:flutter/material.dart';
class ListTask extends StatefulWidget {
const ListTask({Key? key}) : super(key: key);
#override
State<ListTask> createState() => _ListTaskState();
}
class _ListTaskState extends State<ListTask> {
final List<String> tasks = ['masu', 'adasf', 'wfqf', 'santha'];
final TextEditingController _textFieldController = TextEditingController();
void addItemToList() {
setState(() {
tasks.insert(0, _textFieldController.text);
});
}
#override
Widget build(BuildContext context) {
return Container(
height: 320,
width: double.maxFinite,
child: ListView.builder(
padding: EdgeInsets.only(bottom: 10),
itemCount: tasks.length,
itemBuilder: (context, index) {
return Card(
elevation: 1,
color: Colors.grey[200],
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
ExpansionTile(title: Text(tasks[index]), children: <Widget>[
ListTile(
title: Text(tasks[index]),
)
]),
],
),
);
},
),
);
}
Future<void> _displayTextInputDialog(BuildContext context) async {
return showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: Text('TextField in Dialog'),
content: TextField(
onChanged: (value) {
setState(() {
// valueText = value;
});
},
controller: _textFieldController,
decoration: InputDecoration(hintText: "Text Field in Dialog"),
),
actions: <Widget>[
FlatButton(
color: Colors.red,
textColor: Colors.white,
child: Text('CANCEL'),
onPressed: () {
setState(() {
Navigator.pop(context);
});
},
),
FlatButton(
color: Colors.green,
textColor: Colors.white,
child: Text('OK'),
onPressed: () {
setState(() {
addItemToList();
Navigator.pop(context);
});
},
),
],
);
});
}
}
TaskApp Class
import 'package:flutter/material.dart';
import 'package:task_app/Widgets/listtasks.dart';
import 'package:task_app/Widgets/logo.dart';
import 'package:task_app/Widgets/searchbar.dart';
class TaskApp extends StatefulWidget {
const TaskApp({Key? key}) : super(key: key);
#override
State<TaskApp> createState() => _TaskAppState();
}
class _TaskAppState extends State<TaskApp> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Padding(
padding: const EdgeInsets.all(15.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
SizedBox(height: 10),
Logo(),
SizedBox(height: 0),
SearchBar(),
SizedBox(height: 15),
Column(
children: [
Text(
'All tasks',
style: TextStyle(fontWeight: FontWeight.bold, fontSize: 15.0),
)
],
),
SizedBox(height: 15),
ListTask(),
],
),
),
floatingActionButton: FloatingActionButton.extended(
onPressed: () {
_displayTextInputDialog(context);
},
label: const Text('Add Task'),
icon: const Icon(Icons.add),
backgroundColor: Colors.blue[900],
),
);
}
}
Calling point of that method in TaskApp Class:
Method:

You can give this a try, it will call a method defined in ListTask(StatefulWidget) from TaskApp(StatefulWidget) widget.
TaskApp.dart
import 'package:flutter/material.dart';
import 'package:vcare/Screens/tetxing1.dart';
class TaskApp extends StatefulWidget {
final ListTask listTask;
const TaskApp({Key? key,required this.listTask}) : super(key: key);
#override
State<TaskApp> createState() => _TaskAppState();
}
class _TaskAppState extends State<TaskApp> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Padding(
padding: const EdgeInsets.all(15.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
SizedBox(height: 10),
// Logo(),
SizedBox(height: 0),
//SearchBar(),
SizedBox(height: 15),
Column(
children: [
Text(
'All tasks',
style: TextStyle(fontWeight: FontWeight.bold, fontSize: 15.0),
)
],
),
SizedBox(height: 15),
ListTask(),
],
),
),
floatingActionButton: FloatingActionButton.extended(
onPressed: () {
ListTask().method1(context);
},
label: const Text('Add Task'),
icon: const Icon(Icons.add),
backgroundColor: Colors.blue[900],
),
);
}
}
ListTask.dart
import 'package:flutter/material.dart';
class ListTask extends StatefulWidget {
method1(context) => createState().displayTextInputDialog(context);
#override
_ListTaskState createState() => _ListTaskState();
}
class _ListTaskState extends State<ListTask> {
final List<String> tasks = ['masu', 'adasf', 'wfqf', 'santha'];
final TextEditingController _textFieldController = TextEditingController();
void addItemToList() {
setState(() {
tasks.insert(0, _textFieldController.text);
});
}
#override
Widget build(BuildContext context) {
return Container(
height: 320,
width: double.maxFinite,
child: ListView.builder(
padding: EdgeInsets.only(bottom: 10),
itemCount: tasks.length,
itemBuilder: (context, index) {
return Card(
elevation: 1,
color: Colors.grey[200],
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
ExpansionTile(title: Text(tasks[index]), children: <Widget>[
ListTile(
title: Text(tasks[index]),
)
]),
],
),
);
},
),
);
}
Future<void> displayTextInputDialog(BuildContext context) async {
return showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: Text('TextField in Dialog'),
content: TextField(
onChanged: (value) {
setState(() {
// valueText = value;
});
},
controller: _textFieldController,
decoration: InputDecoration(hintText: "Text Field in Dialog"),
),
actions: <Widget>[
FlatButton(
color: Colors.red,
textColor: Colors.white,
child: Text('CANCEL'),
onPressed: () {
setState(() {
Navigator.pop(context);
});
},
),
FlatButton(
color: Colors.green,
textColor: Colors.white,
child: Text('OK'),
onPressed: () {
setState(() {
addItemToList();
Navigator.pop(context);
});
},
),
],
);
});
}
}
if you find this solution helpful please mark as accepted answer

How can i navigate to several new pages using the bottom navigation bar in flutter?

I want to navigate to several new pages using my bottom navigation bar in flutter.
I tried several methods to achieve my requirement. But still neither of them worked out for me. I have attached my relevant entire source code below for a better understanding.
Thank you in advance. :)
Dart Source Code :
class dashboard extends StatefulWidget {
#override
_dashboardState createState() => _dashboardState();
}
// ignore: camel_case_types
class _dashboardState extends State<dashboard> {
#override
Widget build(BuildContext context) {
final authService = Provider.of<AuthService>(context);
return Scaffold(
body: SingleChildScrollView(
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.only(top: 80.0, right: 250),
child: Center(
child: Container(
width: 200.0,
height: 20.0,
decoration:
BoxDecoration(borderRadius: BorderRadius.circular(15.0)),
child: (const Text(
'Hello',
textAlign: TextAlign.center,
style: TextStyle(
fontWeight: FontWeight.bold, color: Colors.black),
)),
),
),
),
Padding(
padding: const EdgeInsets.only(top: 20.0),
child: MaterialButton(
onPressed: () {
Navigator.push(context,
MaterialPageRoute(builder: (context) => profile()));
},
child: const Text('Test'),
),
),
Padding(
padding: EdgeInsets.only(left: 300.0, top: 10.0),
child: IconButton(
icon: new Icon(Icons.notifications),
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => Notifications(),
),
);
},
),
),
Padding(
padding: const EdgeInsets.only(top: 1.0),
child: Center(
child: Container(
width: 390,
height: 450,
decoration: BoxDecoration(
color: Colors.green.shade100,
borderRadius: BorderRadius.circular(10.0)),
),
),
),
],
),
),
floatingActionButton: FloatingActionButton(onPressed: () async {
await authService.signOut();
}),
// : _children[_currentIndex],
bottomNavigationBar: BottomNavigationBar(
type: BottomNavigationBarType.fixed,
items: const [
BottomNavigationBarItem(
icon: Icon(Icons.book_online),
label: 'Page 1',
),
BottomNavigationBarItem(
icon: Icon(Icons.read_more),
label: 'Page 2',
),
BottomNavigationBarItem(
icon: Icon(Icons.account_circle),
label: 'Page 3',
),
],
),
);
}
}

There are many propositions, this is one :
first, you begin by adding a variable index to know where you are. then add a function to change the content of this variable.
class _dashboardState extends State< dashboard > {
int currentIndex = 1;
changeIndex(index) {
setState(() {
currentIndex = index;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: WillPopScope(
child: (currentIndex == 1)
? HomeScreen()
: (currentIndex == 2)
? Screen2()
: (currentIndex == 3)
? Screen3()
: Settings(),
onWillPop: () async {
bool backStatus = onWillPop();
if (backStatus) {
exit(0);
}
return false;
},
),
then link it to the navbar button.
bottomNavigationBar: BottomNavigationBar(
type: BottomNavigationBarType.fixed,
items: const [
InkWell(
onTap: () => changeIndex(1),
child: BottomNavigationBarItem(
icon: Icon(Icons.book_online),
label: 'Page 1',
),
.....
],
),

the return type 'future<bool>' isn't a 'Future<bool>', as required by the closure context

I'm building my quiz app and my quizpage is taking solid shape but here's a problem i have. I added a Willpopscope just so that my users can't go back to the beginning when the quiz has started and it brings up a dialog box. Here's the code:
import 'dart:convert';
//import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
class GetJson extends StatelessWidget {
const GetJson({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return FutureBuilder(
future: DefaultAssetBundle.of(context).loadString("assets/python.json"),
builder: (context, snapshot) {
var mydata = jsonDecode(snapshot.data.toString());
if (mydata == null) {
return Scaffold(
body: Center(
child: Text(
"Loading",
),
),
);
} else {
return QuizPage();
}
},
);
}
}
class QuizPage extends StatefulWidget {
QuizPage({Key? key}) : super(key: key);
#override
_QuizPageState createState() => _QuizPageState();
}
class _QuizPageState extends State<QuizPage> {
Widget choicebutton() {
return Padding(
padding: EdgeInsets.symmetric(
vertical: 10.0,
horizontal: 20.0,
),
child: MaterialButton(
onPressed: () {},
child: Text(
"option 1",
style: TextStyle(
color: Colors.white,
fontFamily: "Alike",
fontSize: 16.0,
),
maxLines: 1,
),
color: Colors.indigo,
splashColor: Colors.indigo[700],
highlightColor: Colors.indigo[700],
minWidth: 200.0,
height: 45.0,
shape:
RoundedRectangleBorder(borderRadius: BorderRadius.circular(20.0)),
),
);
}
#override
Widget build(BuildContext context) {
SystemChrome.setPreferredOrientations(
[DeviceOrientation.portraitDown, DeviceOrientation.portraitUp]);
return WillPopScope(
onWillPop: () {
return showDialog(
context: context,
builder: (context) => AlertDialog(
title: Text(
"Quizstar",
),
content: Text("You Can't Go Back At This Stage"),
actions: [
// ignore: deprecated_member_use
FlatButton(onPressed: () {
Navigator.of(context).pop();
},
child: Text(
"Ok",
),
)
],
)
);
},
child: Scaffold(
body: Column(
children: [
Expanded(
flex: 3,
child: Container(
padding: EdgeInsets.all(15.0),
alignment: Alignment.bottomLeft,
child: Text(
"This is a sample question which will be displayed?",
style: TextStyle(
fontSize: 16.0,
fontFamily: "Quando",
),
),
),
),
Expanded(
flex: 6,
child: Container(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: [
choicebutton(),
choicebutton(),
choicebutton(),
choicebutton(),
],
),
),
),
Expanded(
flex: 1,
child: Container(
alignment: Alignment.topCenter,
child: Center(
child: Text(
"30",
style: TextStyle(
fontSize: 35.0,
fontWeight: FontWeight.w700,
fontFamily: "Times New Roman",
),
),
),
),
),
],
),
),
);
}
}
The error is in the showDialog() but i can't seem to figure it out.
Thanks a lot guys.

This might help
On your willpop scope function do this instead
onWillPop: () {
showDialog(
context: context,
builder: (context) => AlertDialog(
title: Text(
"Quizstar",
),
content: Text("You Can't Go Back At This Stage"),
actions: [
// ignore: deprecated_member_use
FlatButton(onPressed: () {
Navigator.of(context).pop();
},
child: Text(
"Ok",
),
)
],
)
);
return true;
),
child : your widget

Okay i figured it out
return WillPopScope(
onWillPop: () async {
print("Back Button Pressed");
final shouldPop = await showWarning(context);
return shouldPop ?? false;
},
Then i went ahead to define showWarning like this, then defined my dialog box inside it:
Future<bool?> showWarning(BuildContext context) async => showDialog<bool>(
context: context,
builder: (context) => AlertDialog(
title: Text("Quizstar"),
content: Text("You cannot go back at this stage"),
actions: [
ElevatedButton(
onPressed: () => Navigator.pop(context, false),
child: Text("Okay"),
),
//ElevatedButton(
// onPressed: () => Navigator.pop(context, true),
// child: Text("Yes"),
//),
],
),
);
Tips: Don't forget to make the future a bool by writing inside it with it's '?'