How to show SnackBar in ValueNotifier state manager - flutter

Question

I'm working on a PageView with States managed by ValueNotifier. I choose ValuNotifier because it is fast and native. The ValueListenableBuilder works great for a regular page with states like loading, success and error where the body is rebuilt with the content state.
In the code above, ValueListenableBuilder rebuild the body page when state changes, but some states should only push SnackBar and should keep the current value.
What is the best way to handler error (or warning) in SnackBar or Dialog, keeping the body page with the current state (with data, for example)?
All states (even error) carry all data to rebuild the body, than I show SnackBar and rebuild the body;
Show SnackBar by one callback, viewpage will register one controller callback and do all the process to get the context and show SnackBar;
In my point of view, the 2nd distort the ideia of state manager but avoid to rebuild body; but the 1st looks over by the fact I have to carry all information all the time and 'rebuild' everything. I think, the 1st could be a big problem if body has animated transitions.
Do you recomend a 3rd alternative?
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
// ======= Controller =======
class CounterState {}
class SuccessCounterState extends CounterState {
final int currentValue;
SuccessCounterState(this.currentValue);
}
class MaxCounterState extends CounterState {}
class MinCounterState extends CounterState {}
class Counter extends ValueNotifier<CounterState> {
Counter() : super(SuccessCounterState(0));
var _localValue = 0;
void increment() {
if (_localValue + 1 > 9) {
value = MaxCounterState();
} else {
_localValue++;
value = SuccessCounterState(_localValue);
}
}
void decrement() {
if (_localValue - 1 < 0) {
value = MinCounterState();
} else {
_localValue--;
value = SuccessCounterState(_localValue);
}
}
}
// ==== Page ====
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
#override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final counter = 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:',
),
ValueListenableBuilder<CounterState>(
valueListenable: counter,
builder: (BuildContext context, state, _) {
if (state is SuccessCounterState) {
return Text(
'${state.currentValue}',
style: Theme.of(context).textTheme.headline4,
);
}
if (state is MaxCounterState) {
Future.delayed(const Duration(milliseconds: 1), () {
const snackBar =
SnackBar(content: Text('Reached the max value'));
ScaffoldMessenger.of(context).showSnackBar(snackBar);
});
}
if (state is MinCounterState) {
Future.delayed(const Duration(milliseconds: 1), () {
const snackBar =
SnackBar(content: Text('Reached the min value'));
ScaffoldMessenger.of(context).showSnackBar(snackBar);
});
}
return const SizedBox();
},
),
],
),
),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: [
FloatingActionButton(
onPressed: counter.decrement,
tooltip: 'Decrement',
child: const Icon(Icons.remove),
),
const SizedBox(width: 20.0),
FloatingActionButton(
onPressed: counter.increment,
tooltip: 'Increment',
child: const Icon(Icons.add),
),
],
),
);
}
}