Error saying 1 required argument(s) expected but 0 found. On every flutter project the Column gives an error. Opened up a new flutter project on VS code and still gives the same error.
have updated dart, uninstalled flutter and dart on VS and installed again, my flutter doctor runs completely fine.
import package:flutter/material.dart
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
child: Column(
mainAxisAlignment: MainAxisAlignment.center ,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
1 required argument(s) expected, but 0 found. Try adding the additional required arguments.
Here is the full code, replace yours with mine.
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
Related
The following code is from an example from "dartpad.dev" web site. Within the class MyHomePage extends StatefulWidget { ..., in constructor part, I can't understand what's going on. I've been studying dart for a reasonable time, but still it's hard for me to figure out what's happenning. required this.title is OK, however why there are Key? key and : super(key: key) ?
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
final String title;
const MyHomePage({
Key? key,
required this.title,
}) : super(key: key);
#override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
const Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: const Icon(Icons.add),
),
);
}
}
In my Flutter project, I have the default Flutter code in home screen to update a counter by floating action button press. Here's the code of that class-
main.dart
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key? key, required this.title}) : super(key: key);
String title;
#override
State<MyHomePage> createState() => MyHomePageState();
}
class MyHomePageState extends State<MyHomePage> {
int counter = 0;
void _incrementCounter() {
setState(() {
counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text(
'You have pushed the button this many times:',
),
Text(
'$counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: UpdateWidget().showButton()
),
);
}
}
Now, I just wanted to update the counter(state variable) without making it static from a new class named UpdateWidget.
I have tried updating the variable like this way:
UpdateWidget.dart
class UpdateWidget extends StatefulWidget {
UpdateWidget({Key? key}) : super(key: key);
#override
_UpdateWidgetState createState() => _UpdateWidgetState();
GlobalKey<MyHomePageState> homeKey = GlobalKey();
Widget showButton() {
return FlatButton(
onPressed: () {
MyHomePage(key: homeKey, title: 'Hello',);
debugPrint('pressed');
homeKey.currentState?.counter = 5;
}, child: const Text('A'),
);
}
}
class _UpdateWidgetState extends State<UpdateWidget> {
double defaultScreenWidth = 400.0;
double defaultScreenHeight = 810.0;
#override
Widget build(BuildContext context) {
return const Scaffold(
body: Center(
child: Text(''),
),
);
}
}
In, UpdateWidget class, inside FlatButton onPressed block, the print message is showing but it is not updating the counter variable like the way I wanted.
So, I need a way to update this variable and show that in UI.
I am currently working on an app; I want to change the value of a String which is declared in another dart file and then pass that changed state to the stateful widget.
I.E;
I create a file called as "Body.dart" file where I have declared a String called as 'scale' who's value initially is "Empty".
Later when a button in another dart file "scale_button" is pressed, I want to assign the string scale = "Hello" in my Body.dart file. So that the stateful widget also displays the same on the screen.
You can use provider(or any other state management) package in that case. In yaml file add, provider: ^4.3.2+4
class HomeApp extends StatefulWidget {
#override
_HomeAppState createState() => _HomeAppState();
}
class _HomeAppState extends State<HomeApp> {
StringProvider _stringProvider;
#override
void initState() {
super.initState();
_stringProvider = Provider.of<StringProvider>(context, listen: false);
}
void updateString() {
_stringProvider.setString('hai');
}
#override
Widget build(BuildContext context) {
StringProvider _stringProvider = Provider.of<StringProvider>(context);
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Container(
child: Text(
_stringProvider.str,
style: TextStyle(
fontSize: 22,
),
),
),
RaisedButton(
onPressed: updateString,
child: Text('Click'),
),
],
),
),
);
}
}
// class for storing data(StringProvider.dart)
import 'package:flutter/material.dart';
class StringProvider extends ChangeNotifier { // create a common file for data
String _str = 'hello';
String get str => _str;
void setString(String st) {
_str = st;
notifyListeners();
}
}
When you create a new Flutter project the sample code of the counter shows you how to do this. Check out the comments in the next code:
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
// here is passing a String to MyHomePage.
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
// And here you can see how to make the widget wait for a variable
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
Full code of Sample Counter App
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
I am having a problem with the NotificationListener in flutter. I've build a simple testing app because I am struggling with it.
After clicking on the FlatButton the Notification should be dispatched and then caught by the NotificationListener in onNotification.
So the expected console output would be:
"TestNot"
"Bubble"
But all I am getting is "TestNot".
So the notification is not caught by the listener.
Any idea what I could be doing wrong?
Thank you :-)
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyNotification extends Notification {
final String title;
const MyNotification({this.title});
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: NotificationListener<MyNotification>(
onNotification: (notification) {
print("Bubble");
return true;
},
child: Center(
child: Column(
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
FlatButton(onPressed: () {print("TestNot"); MyNotification(title: "TestNot").dispatch(context);}, child: Text("TestNot")),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
)),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
When you need a child to notify its parent, you can use NotificationListener.
But, when you need communications to be implemented inversely, in other words, a parent to notify its children, you can use ValueListenableBuilder
A nice doc about it available here:
https://medium.com/flutter-community/flutter-notifications-bubble-up-and-values-go-down-c1a499d22d5f
"Flutter, notifications ‘bubble up’ and values ‘go down’"
You cannot receive the notification at the same level of where it was dispatched. Please refer to docs : https://api.flutter.dev/flutter/widgets/NotificationListener-class.html
NotificationListener class :
A widget that listens for Notifications bubbling up the tree.
I've updated your code to make it work.
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyNotification extends Notification {
final String title;
const MyNotification({this.title});
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: NotificationListener<MyNotification>(
onNotification: (MyNotification notification) {
print("Bubble");
return true;
},
child: Center(
child: Column(
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
MyChild(),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
)),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
class MyChild extends StatelessWidget {
#override
Widget build(BuildContext context) {
return FlatButton(
onPressed: () {
print("TestNot");
MyNotification(title: "TestNot").dispatch(context);
},
child: Text("TestNot"));
}
}
I'm pretty new on Flutter and I trying to build a desktop app.
I did all steps of following guide: https://medium.com/flutter-community/flutter-from-mobile-to-desktop-93635e8de64e (Running your own project (compiling the Go desktop project))
Unfornatelly, when I try to run the code I have this error:
NoSuchMethodError: Class "Window" has no instance getter 'locales'
Receiver: Instance of Window
Tried calling: locales
Thank you in advance
The Operating System is Windows 8.1 and following the code. It is the starter one where I just added the debugDefaultTargetPlatformOverride part.
import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart' show
debugDefaultTargetPlatformOverride;
void main(){
debugDefaultTargetPlatformOverride = TargetPlatform.fuchsia;
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
methods.
);
}
}