knobs.dart

WidgetbookUseCase(
  name: 'Usecase1',
  builder: (BuildContext context) {
    final width = context.knobs.double.slider(
        label: 'width', min: 10, max: 100, initialValue: 50);
    final height = context.knobs.double.slider(
        label: 'height', min: 10, max: 100, initialValue: 50);

    return Scaffold(
      body: Center(
        child: Container(
          color: Colors.purpleAccent,
          width: width,
          height: height,
        ),
      ),
    );
  },
),