1. Dart
2. dart:async
3. ZoneSpecification
4. registerCallback property

##### ZoneSpecification class

1. Constructors
2. ZoneSpecification
3. from
4. Properties
5. createPeriodicTimer
6. createTimer
7. errorCallback
8. fork
9. handleUncaughtError
10. hashCode
11. print
12. registerBinaryCallback
13. registerCallback
14. registerUnaryCallback
15. run
16. runBinary
17. runtimeType
18. runUnary
19. scheduleMicrotask
20. Methods
21. noSuchMethod
22. toString
23. Operators
24. operator ==

description

# registerCallback property Null safety

(ZoneCallback<R> Function<R>?(Zone self, ZoneDelegate parent, Zone zone, R f())?) registerCallback

## Implementation

    RegisterCallbackHandler? get registerCallback;