RouteObserver<R extends Route> constructor Null safety

1. Flutter
2. widgets
3. RouteObserver<R extends Route>
4. RouteObserver constructor

RouteObserver class

1. Constructors
2. RouteObserver
3. Properties
4. hashCode
5. navigator
6. runtimeType
7. Methods
8. debugObservingRoute
9. didPop
10. didPush
11. didRemove
12. didReplace
13. didStartUserGesture
14. didStopUserGesture
15. noSuchMethod
16. subscribe
17. toString
18. unsubscribe
19. Operators
20. operator ==