I am stuck on this one null error, I cannot fix this error that reads "error: The argument type 'Null' can't be assigned to the parameter type 'int'." The error shows up at the selected: null, line. I have added my code below hopefully someone can help. Let me know if any other code is needed.
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () async {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => StudyPage(
title: 'Add a study',
selected: null,
)));
addition
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();
},
)
],
);
}
);
}
}
CodePudding user response：
You can't pass null to a nonnull property
class StudyPage extends StatefulWidget {
final String title;
final int selected;
.....
change to
class StudyPage extends StatefulWidget {
final String title;
final int? selected; <<<-----
CodePudding user response：
You have to specify the selected argument of StudyPage as nullable. To do so
edit this code:
class StudyPage extends StatefulWidget {
final String title;
final int selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
And change it to
class StudyPage extends StatefulWidget {
final String title;
final int? selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
CodePudding user response：
In your study_page.dart add '?' to make selected optional data type which will accept both int and null values.
class StudyPage extends StatefulWidget {
final String title;
final int? selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
In your StudyViewModel make studies parameter an optional int? studies;