Dart APIunself_componentUnSliverArtBaremoji emoji property Null safety Widget emoji final Implementation final Widget emoji; unself_component unself_component UnSliverArtBar emoji property UnSliverArtBar class Constructors UnSliverArtBar Properties action background description emoji hashCode isImmersive key leading name runtimeType trailing Methods createElement createState debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==