From child set state of other child component - dart

Question

Let's say we have class Car (Stateless) that have inside it two class for now it will be Wheel (Statefull) and Mask (Statefull) and my job is to whenever state of class Wheel is changed call class Mask to change it state also with specific data from Wheel, but parent should have also access to child data. How can I achieve it?
import 'package:flutter/material.dart';
void main() {
runApp(Car());
}
class Car extends StatelessWidget {
int childMaskVal = ..??????
#override
Widget build(BuildContext context) {
return Container(
child: Scaffold(
appBar: AppBar(
title: Text('App bar'),
),
body: Column(
children: <Widget>[
Wheel(),
Mask(),
],
),
),
);
}
}
class Wheel extends StatefulWidget {
_WheelState createState() => _WheelState();
}
class _WheelState extends State<Wheel> {
int _value = 0;
#override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
RaisedButton(
onPressed: () {
setState(() {
_value++;
});
},
),
Text(_value.toString()),
],
),
);
}
}
class Mask extends StatefulWidget {
_MaskState createState() => _MaskState();
}
class _MaskState extends State<Mask> {
int _value = 13;
#override
Widget build(BuildContext context) {
return Container(
child: Text((_value * Wheel._value).toString()),???????
);
}
}

Answer 1

You can pass the callback to the child.
In the example you provided, the parent should be a statefulWidget and the children should be a stateless widget. You should initialize the state in the parent and then pass it to the child.
If you find that the parent needs to access the data in the child, that means you need to move the state up.
See the example below:
import 'package:flutter/material.dart';
void main() {
runApp(Car());
}
class Car extends StatefulWidget{
#override
_CarState createState() => _CarState();
}
class _CarState extends State<Car> {
int childMaskVal = ..??????
int _value = 1;
#override
Widget build(BuildContext context) {
return Container(
child: Scaffold(
appBar: AppBar(
title: Text('App bar'),
),
body: Column(
children: <Widget>[
Wheel(
value: _value,
onPressed: () {
setState(() {
_value++;
// update state here
})
}),
Mask(),
],
),
),
);
}
}
class Wheel extends Stateless {
int value;
Function onPressed;
Wheel({this.value, this.onPresed})
#override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
RaisedButton(
onPressed: onPressed
),
Text(value.toString()),
],
),
);
}
}
You can also check this post How to pass data from child widget to its parent