Dart APIunself_componentFloatContainerchild child property Null safety Widget? child final Implementation final Widget? child; unself_component unself_component FloatContainer child property FloatContainer class Constructors FloatContainer Properties child hashCode key padding runtimeType Methods build createElement debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==