Dart APIunself_componentUnSheetpreviousRouteAnimationCurve previousRouteAnimationCurve property Null safety Curve? previousRouteAnimationCurve final Implementation final Curve? previousRouteAnimationCurve; unself_component unself_component UnSheet<T> previousRouteAnimationCurve property UnSheet class Constructors UnSheet Properties animationCurve arguments backgroundColor barrierColor bounce child clipBehavior closeProgressThreshold duration elevation enableDrag expand hashCode isDismissible key name overlayStyle previousRouteAnimationCurve restorationId runtimeType secondAnimation settings shadow shape topRadius transitionBackgroundColor useRootNavigator Methods canUpdate createRoute noSuchMethod toString Operators operator ==