EpoxySample.kt

interface EpoxyModelClickListener {
    fun onPriceChanged(price: Double)
}

class HeaderEpoxyModel : Epoxy {
    @EpoxyAttribute
    var double price = 0.0
    @EpoxyAttribute
    var EpoxyModelClickListener clickListener? = null

    override fun bind(holder: ViewHolder) {
        // consider to use abstract epoxy model for price updating

        holder.text.setText(price.toString)
        // trigger price change from user
        holder.text.setOnClickListener {
            // emit new price to listener
            clickListener?.onPriceChanged(price)
        }
    }

}

class ItemEpoxyModel : Epoxy {
    @EpoxyAttribute
    var double price = 0.0
    @EpoxyAttribute
    ...

    override fun bind(holder: ViewHolder) {
        // the price part is as same as header

        holder.text.setText(price.toString)
        // trigger price change from user
        holder.text.setOnClickListener {
            // emit new price to listener
            clickListener?.onPriceChanged(price)
        }
    }
    
}

class MyEpoxyController(private val clickListener: EpoxyModelClickListener) : EpoxyController() {

    var price by Delegates.observable<Double>(0.0) { _, _, _ ->
        requestModelBuild()
    }

    override fun buildModels() {
        headerEpoxyModel()
            .price(price)
            .clickListener(clickListener)
        itemEpoxyModel()
            .price(price)
            .clickListener(clickListener)
    }
}

class ViewModel {

    private val _price = MutableLiveData<Double>
    val price: LiveData<Double> = _price

    fun updatePrice(price: Double) {
        _price.value = price
    }
}

class MyFragment : EpoxyModelClickListener {
    private val viewModel by inject()
    private MyEpoxyController controller by lazy {
        MyEpoxyController(this).apply {
            viewModel.price.observe {
                this.requestModelBuild()
            }
        }
    }

    @override
    fun onPriceChanged(price: Double) {
        viewModel.updatePrice(price)
    }
}