SelectionContainerDelegate constructor Null safety

1. Flutter
2. widgets
3. SelectionContainerDelegate
4. SelectionContainerDelegate constructor

SelectionContainerDelegate class

1. Constructors
2. SelectionContainerDelegate
3. Properties
4. containerSize
5. hashCode
6. runtimeType
7. value
8. Methods
9. add
10. addListener
11. dispatchSelectionEvent
12. getSelectedContent
13. getTransformFrom
14. getTransformTo
15. noSuchMethod
16. pushHandleLayers
17. remove
18. removeListener
19. toString
20. Operators
21. operator ==