Provider Scope

MaterialApp
 > provider(Screen A)
 > Screen B

If Provider is instantiated in Screen A, it won’t be accessible in Screen B after a Navigator.push from A → B.

Why?

Because Provider is an InheritedWidget and Navigator uses MaterialApp context outside its Screen A context scope. (See Details below.)

Fix

Moving Provider up to a common-parent, MaterialApp context, allows both Screen A and B to inherit its state/context.

provider(MaterialApp)
 > Screen A
 > Screen B

Example

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    /// wrap MaterialApp in Provider widget
    return ChangeNotifierProvider(
      create: (context) => ColorModel(), // ← create/init your state model
      child: MaterialApp(
          home: ScreenA()
      ),
    );
  }
}

Details

Provider

• Provider is based on InheritedWidget. Only child widgets can inherit parent widget’s state.

  • Provider needs to be the root widget for any widget tree that wants access to your “provided” state object.

Navigator

• Navigator.push(context) on Screen A doesn’t use the context from Screen A.
  • It uses context from MaterialApp.
• Navigator.push(context) is actually Navigator.of(context).push
• Navigator.of(context) means: search up this context hierarchy until you find a context that instantiated a Navigator
  • A default Navigator is instantiated in MaterialApp.
  • Unless you explicitly create/use a different Navigator, you’re using the default.
  • Navigator‘s context is that of MaterialApp.
• Screen B will get that context (of MaterialApp), not the context of Screen A.
  • B is a sibling of A, not its child.
  • B does not inherit from A, even though it appears “instantiated” inside context A.
  • Screen B is a child of MaterialApp context, not of Screen A context.
  • Provider context scope, if defined in Screen A, doesn’t cover Screen B

Screen A → B

Navigator.push(context, MaterialPageRoute(builder: (context) => ScreenB()))

is actually:

Navigator.of(context).push(MaterialPageRoute(builder: (context) => ScreenB()))

which is like:

Navigator.of(MaterialApp).push(
  MaterialPageRoute(builder: (MaterialAppContext) => ScreenB())
)

So Screen B is under MaterialApp context, not under Screen A context and therefore has no access to Screen A Provider and its context.

See this answer for a code sample to a similar question about Provider.