indexedStack內控制indexedStack外的widget (e.g. in stack to nav push a page out of stack)

! use provider to save the context 

let NavBar is the widget out of the indexedStack

-create NavBarVM and let it be a provider

-create a variable "navBarContext" in NavBarVM

-create the function "setNavBarContext" & "getNavBarContext"

-when navbar build:

build(BuildContext context) {

setNavBarContext(context);

}

something like that

-in the indexedStack widget

BuildContext navBarContext = context.read<NavbarVM>().getNavBarContext();

Navigator.push(

  navBarContext,

  MaterialPageRoute(

      builder: (navBarContext) =>

          SecondPage()

  ),

);