ZoomProvider constructor Null safety

1. diginote
2. zoom_provider
3. ZoomProvider
4. ZoomProvider constructor

ZoomProvider class

1. Constructors
2. ZoomProvider
3. Properties
4. hashCode
5. hasListeners
6. runtimeType
7. zoom
8. Methods
9. addListener
10. dispose
11. noSuchMethod
12. notifyListeners
13. removeListener
14. toString
15. zoomIn
16. zoomOut
17. Operators
18. operator ==
19. Constants
20. maxZoom
21. minZoom
22. zoomAmount