1. @override
void debugFillProperties(DiagnosticPropertiesBuilder description)

Source

@override
void debugFillProperties(DiagnosticPropertiesBuilder description) {
  super.debugFillProperties(description);
  description.add(new DiagnosticsProperty<Widget>('icon', icon, showName: false));
  description.add(new ObjectFlagProperty<VoidCallback>('onPressed', onPressed, ifNull: 'disabled'));
  description.add(new StringProperty('tooltip', tooltip, defaultValue: null, quoted: false));
}