RangeError (index) Flutter - flutter

Question

I am getting an error and red screen while trying to click a button. RangeError (index): Invalid value: Valid value range is empty: 0. I do not know how to fix this error because nothing is flagged until I run my emulator. I have attached my
If I need to add some code please let me know I am more than willing to. Thank you!
home_page.dart
import 'package:flutter/material.dart';
import 'package:timestudy_test/pages/study_page.dart';
import 'package:timestudy_test/pages/timer_page.dart';
import 'package:timestudy_test/viewmodels/study_viewmodel.dart';
class HomePage extends StatefulWidget {
#override
State createState() => HomePageState();
}
class HomePageState extends State<HomePage> {
TextEditingController textController = new TextEditingController();
late String filter;
#override
void initState() {
textController.addListener(() {
setState(() {
filter = textController.text;
});
});
super.initState();
}
#override
void dispose() {
textController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Scaffold(
resizeToAvoidBottomInset: false,
appBar: AppBar(
title: Text('TimeStudyApp'),
),
body: Material(
child: Column(
children: <Widget>[
Padding(
padding: EdgeInsets.only(top: 8.0, left: 16.0, right: 16.0),
child: TextField(
style: TextStyle(fontSize: 18.0),
decoration: InputDecoration(
prefixIcon: Icon(Icons.search),
suffixIcon: IconButton(
icon: Icon(Icons.close),
onPressed: () {
textController.clear();
FocusScope.of(context).requestFocus(FocusNode());
},
),
hintText: "Search...",
),
controller: textController,
)),
Expanded(
child: StudyViewModel.studies.length > 0
? ListView.builder(
itemCount: StudyViewModel.studies.length,
itemBuilder: (BuildContext context, int index) {
if (filter == null || filter == "") {
return buildRow(context, index);
} else {
if (StudyViewModel.studies[index].name
.toLowerCase()
.contains(filter.toLowerCase())) {
return buildRow(context, index);
} else {
return Container();
}
}
},
)
: Center(
child: Text('No studies found!'),
),
)
],
),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () async {
int? nullableInterger;
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => StudyPage(
title: 'Add a study',
selected: nullableInterger ?? 0,
)));
},
),
);
}
Widget buildRow(BuildContext context, int index) {
return ExpansionTile(
title: Text(StudyViewModel.studies[index].name, style: TextStyle(fontSize: 18.0)),
children: <Widget>[
ListView.builder(
shrinkWrap: true,
physics: ClampingScrollPhysics(),
itemCount: StudyViewModel.studies[index].tasks.length,
itemBuilder: (context, int taskIndex) {
return ListTile(
title: Text(StudyViewModel.studies[index].tasks[taskIndex].name),
contentPadding: EdgeInsets.symmetric(horizontal: 32.0),
subtitle: Text(
StudyViewModel.studies[index].tasks[taskIndex].elapsedTime),
trailing: IconButton(
icon: Icon(
Icons.timer
),
onPressed: () async {
await Navigator.push(
context,
MaterialPageRoute(
builder: (context) => TimerPage(
task: StudyViewModel
.studies[index].tasks[taskIndex])));
},
),
);
},
),
Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
IconButton(
icon: Icon(
Icons.edit
),
onPressed: () async {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => StudyPage(
title: StudyViewModel.studies[index].name,
selected: index)));
},
),
IconButton(
icon: Icon(
Icons.delete
),
onPressed: () async {
await showDialog(
context: context,
builder: (context) {
return AlertDialog(
content: Text('Do you wish to delete this study?'),
actions: <Widget>[
FlatButton(
child: Text('Accept'),
onPressed: () async {
StudyViewModel.studies.removeAt(index);
await StudyViewModel.saveFile();
Navigator.of(context).pop();
},
),
FlatButton(
child: Text('Cancel'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
);
});
},
),
],
),
],
);
}
}
study_page.dart
import 'package:flutter/material.dart';
import 'package:timestudy_test/models/study.dart';
import 'package:timestudy_test/models/task.dart';
import 'package:timestudy_test/viewmodels/study_viewmodel.dart';
class StudyPage extends StatefulWidget {
final String title;
final int selected;
StudyPage({required this.title, required this.selected});
#override
State createState() => StudyPageState();
}
class StudyPageState extends State<StudyPage> {
late Study study;
late TextField nameField;
TextEditingController nameController = new TextEditingController();
late TextField taskNameField;
TextEditingController taskNameController = new TextEditingController();
#override
void initState() {
nameField = new TextField(
controller: nameController,
decoration: InputDecoration(
labelText: 'Study name'),
);
taskNameField = new TextField(
controller: taskNameController,
decoration:
InputDecoration(labelText: 'Task name'),
);
if(widget.selected != null) {
study = StudyViewModel.studies[widget.selected];
nameController.text = study.name;
} else {
study = new Study(
name: "",
tasks: <Task>[]
);
}
super.initState();
}
#override
void dispose() {
nameController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Scaffold(
resizeToAvoidBottomInset: false,
appBar: AppBar(
title: Text(widget.title),
),
body: Material(
child: Padding(padding: EdgeInsets.all(16.0), child: Column(
children: <Widget>[
Padding(padding: EdgeInsets.only(bottom: 8.0), child: nameField),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text('Tasks:', style: TextStyle(fontSize: 18.0),),
IconButton(
icon: Icon(Icons.add),
onPressed: () async {
await showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: Text('Add a task'),
content: taskNameField,
actions: <Widget>[
FlatButton(
child: Text('Cancel'),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: Text('Accept'),
onPressed: () {
if(taskNameController.text == ""){
errorDialog(context, 'Please enter a task name!');
} else {
setState(() {
study.tasks.add(new Task(
name: taskNameController.text,
elapsedTime:
StudyViewModel.milliToElapsedString(
0)));
taskNameController.clear();
});
Navigator.of(context).pop();
}
},
),
],
);
});
},
)
],
),
Expanded(
child: ListView.builder(
itemCount: study.tasks.length,
itemBuilder: (context, int index) {
return ListTile(
title: Text(study.tasks[index].name),
trailing: IconButton(
icon: Icon(Icons.delete),
onPressed: () {
setState(() {
study.tasks.removeAt(index);
});
},
),
);
},
),
), Spacer(),
Center(
child: RaisedButton(
color: Theme.of(context).accentColor,
child: Text('Save'),
onPressed: () async {
if (nameController.text == "") {
errorDialog(context, 'Please enter a study name!');
} else {
if (study.tasks.length < 1) {
errorDialog(context, 'Please add at least one task!');
} else {
study.name = nameController.text;
if (widget.selected != null) {
StudyViewModel.studies[widget.selected] = study;
await StudyViewModel.saveFile();
Navigator.of(context).pop();
} else {
if (StudyViewModel.checkName(nameController.text)) {
errorDialog(context, 'Study name already taken!');
} else {
StudyViewModel.studies.add(study);
await StudyViewModel.saveFile();
Navigator.of(context).pop();
}
}
}
}
},
))
],
),
)));
}
void errorDialog(BuildContext context, String message) async {
await showDialog(
context: context,
builder: (context) {
return AlertDialog(
content: Text(message),
actions: <Widget>[
FlatButton(
child: Text('Close'),
onPressed: () {
Navigator.of(context).pop();
},
)
],
);
}
);
}
}

Answer 1

floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () async {
int? nullableInterger;
// the issue is here you need to assign value
// the nullableInterger is use here as nothing.. declare it on state level and
// assign it when your listview builder done so the value of nullable integer is
// changed and passing value as argument will not be 0 and this error will not appear again
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => StudyPage(
title: 'Add a study',
selected: nullableInterger ?? 0,
)));
},
),