Visibility는 물리적 공간을 차지하면서 show/hide만 하지만
Offstage는 물리적 공간까지도 show/hide 해준다 (강추)
참고::https://stackoverflow.com/questions/44489804/show-hide-widgets-in-flutter-programmatically
Try the Offstage widget
if attribute offstage:true the not occupy the physical space and invisible,
if attribute offstage:false it will occupy the physical space and visible
Offstage(
offstage: true,
child: Text("Visible"),
),Opacity, which can stop its child from being painted.
Offstage, which can stop its child from being laid out or painted.
TickerMode, which can stop its child from being animated.
ExcludeSemantics, which can hide the child from accessibility tools.
IgnorePointer, which can disable touch interactions with the child.
Visibility 참고 자료
https://api.flutter.dev/flutter/widgets/Visibility-class.html
Offstage 참고 자료
https://api.flutter.dev/flutter/widgets/Offstage-class.html
