callback.kt

private fun providePropertyChangedCallback(): OnPropertyChangedCallback {
   return object : OnPropertyChangedCallback() 
      override fun onPropertyChanged(sender: Observable?, propertyId: Int) {
          val product = sender as Product
          
          viewModel.setDataMediatorValue (
            !(product.quantity == null || product.quantity == 0 ||
              product.weight.isNullOrEmpty() || 
              (product.weight ?: "0.00").toDouble() == 0.00
           )
        }
     }
 }