Invoking setState on child Stateful from parent Stateful widget - flutter

Question

When I am invoking setState in child stateful widget. it is showing an error or warning. Is there any way to call Stateful widget inside Stateful widget without causing an error or any good way to do the same?
Here is my sample code :
parent.dart
class Parent extends StatefulWidget {
#override
_ParentState createState() => _ParentState();
}
class _ParentState extends State<Parent> {
var title = "Parent";
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: ListView(
children: <Widget>[
Text(title),
Child(init:true), // <-- Calling Child Widget
],
),
),
);
}
}
child.dart
class Child extends StatefulWidget {
final bool init; // <- Showing warning on removing 'final'
// This class (or a class that this class inherits from) is marked as '#immutable', but one or more of its instance fields aren't final: Child.init
Child({
Key? key,
required this.init,
}) : super(key: key);
#override
_ChildState createState() => _ChildState();
}
class _ChildState extends State<Child> {
#override
Widget build(BuildContext context) {
return Container(
color: widget.init ? Colors.red : Colors.blue,
child: TextButton(
onPressed: () {
setState(
() {
// widget.init = false;
// want to change 'wiget.init' but its final
// removing final causing warning
},
);
},
child: Text("Click me"),
),
);
}
}

Answer 1

You can pass function that changes init variable.
class Parent extends StatefulWidget {
#override
_ParentState createState() => _ParentState();
}
class _ParentState extends State<Parent> {
var title = "Parent";
var init = true;
void setInitFalse(){
setState((){
init = false;
})
}
bool getInit(){
return init;
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: ListView(
children: <Widget>[
Text(title),
Child(init: getInit(), setInitFalse: setInitFalse()),
],
),
),
);
}
}
And then in child
class Child extends StatefulWidget {
final Function init; // <- Showing warning on removing 'final'
// This class (or a class that this class inherits from) is marked as '#immutable', but one or more of its instance fields aren't final: Child.init
final Function setInitFalse;
Child({
Key? key,
required this.init,
required this.setInitFalse
}) : super(key: key);
#override
_ChildState createState() => _ChildState();
}
class _ChildState extends State<Child> {
#override
Widget build(BuildContext context) {
return Container(
color: widget.init() ? Colors.red : Colors.blue,
child: TextButton(
onPressed: () {
widget.setInitFalse();
},
child: Text("Click me"),
),
);
}
}