Error when ChangeNotifierProvider and MaterialPageRoute used together
Solution 1:
It is because you are using child in provider, which means the widget won't build upon the provider.
You should use builder:
ChangeNotifierProvider<A>.value(
value: a,
builder: (context, child) => const NewPage(),
);
Now the provider are able to inject the dependency(A), and rebuild your desired widget(NewPage) with the correct context.