factory property Null safety

1. jrpn
2. jrpn15.main
3. ButtonLayout15
4. factory property

ButtonLayout15 class

1. Constructors
2. ButtonLayout15
3. Properties
4. bsp
5. chs
6. cos
7. div
8. dot
9. eex
10. enter
11. eX
12. factory
13. fShift
14. gsb
15. gShift
16. gto
17. hashCode
18. landscapeLayout
19. minus
20. mult
21. n0
22. n1
23. n2
24. n3
25. n4
26. n5
27. n6
28. n7
29. n8
30. n9
31. onOff
32. plus
33. portraitLayout
34. rcl
35. rdown
36. reciprocal
37. rs
38. runtimeType
39. sin
40. sqrt
41. sst
42. sto
43. sum
44. tan
45. tenX
46. xy
47. yX
48. Methods
49. noSuchMethod
50. toString
51. Operators
52. operator ==