Provider's watch() dosen't catch changing state in flutter - flutter

Question

I am studying, provider in flutter. I try to make login process by using beamer and provider.
If user's auth state that is dectected by Provider context.watch<AuthenticationNotifier>().isAuthenticated; is false, BeamGuard force user to go auth screen.
final _routerDelegate = BeamerDelegate(
guards: [
BeamGuard(
pathPatterns: ['/'],
check: (context, location) {
return context.watch<AuthenticationNotifier>().isAuthenticated;
},
beamToNamed: (origin, target) => '/auth',
)
],
locationBuilder: BeamerLocationBuilder(
beamLocations: [PostListLocations(), AuthLocations()]),
);
User click login button in auth screen, auth state change true. I checked user'auth state is changed in AuthScreen.
void attemptVerify(BuildContext context) {
var authNotifier = context.read<AuthenticationNotifier>();
authNotifier.setUserAuth(true);
logger.d(authNotifier.userState);
}
}
but provider in BeamGuard is not watch state change. user do not go to main page, stay in auth page. if i set user's auth state True, user go to directly main page.So I think beamer is not problem. I think Provider doesn't work. I cannot find my mistake. could you help me?
this is full code.
main.dart
final _routerDelegate = BeamerDelegate(
guards: [
BeamGuard(
pathPatterns: ['/'],
check: (context, location) {
return context.watch<AuthenticationNotifier>().isAuthenticated;
},
beamToNamed: (origin, target) => '/auth',
)
],
locationBuilder: BeamerLocationBuilder(
beamLocations: [PostListLocations(), AuthLocations()]),
);
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return ScreenUtilInit(
designSize: const Size(375, 812),
builder: (BuildContext context, Widget? child) {
return ChangeNotifierProvider<AuthenticationNotifier>( //provider
create: (context) => AuthenticationNotifier(),
child: MaterialApp.router(
routeInformationParser: BeamerParser(),
routerDelegate: _routerDelegate,
),
);
},
);
}
}
auth_notifier.dart
import 'package:flutter/widgets.dart';
class AuthenticationNotifier extends ChangeNotifier {
bool _isAuthenticated = false;
bool get isAuthenticated => _isAuthenticated;
void setUserAuth(bool authState) {
_isAuthenticated = authState;
notifyListeners();
}
}
auth_scree.dart
class AuthScreen extends StatefulWidget {
const AuthScreen({Key? key}) : super(key: key);
#override
State<AuthScreen> createState() => _AuthScreenState();
}
class _AuthScreenState extends State<AuthScreen> {
#override
Widget build(BuildContext context) {
return SafeArea(
child: GestureDetector(
onTap: () {
FocusScope.of(context).unfocus();
},
child: Scaffold(
body: SingleChildScrollView(
child: ElevatedButton(
onPressed: () {
attemptVerify(context);
},
child: Text("button"),
),
)),
),
);
}
void attemptVerify(BuildContext context) {
var authNotifier = context.read<AuthenticationNotifier>();
authNotifier.setUserAuth(true);
}
}