Shows a possible example for using a TypedEpoxyController with the currentData property. Not sure if this is best pracitce.

EpoxyController.kt

class MyEpoxyController : TypedEpoxyController<ViewState> {
  /**
   * This buildModels method takes in the current ViewState and builds all of the Epoxy Models
   * that need to be displayed for this state.
   */
  override fun buildModels(data: ViewState) {
    data.usersAndItems.forEach { userItems ->
      addUserItemsModels(userItems)
    }
  }
  
  /**
   * Given a user and their items, put the user row first followed by each item they have.
   */
  private fun addUserItemsModels(userItems: UserItems) {
    addUserModel(userItems.user)
    
    userItems.items.forEach { item ->
      addItemModel(item)
    }
  }
  
  /**
   * This is where I become unsure of best practice. I don't want to reference `currentData` here because it's nullable.
   * The alternative is to pass the state all the way through from the call to `buildModels` but that feels tedious.
   *
   * The second concern, is how do I unit test this class? Should I use robolectric, or should I pull out this
   * model building logic into a separate class that I can write regular Junit tests for?
   */
  private fun addItemModel(item: Item) {
    val isInBag = currentData?.cartItems?.items?.contains(item) == true
    
    ItemModel_()
      .inBag(isInBag)
      .addTo(this)
  }
}

Models.kt

/**
 * This maps a single User with all of the Items that are associated with that user.
 */
data class UserItems(
  val user: User,
  val items: List<Item>
)

/**
 * Maintains all of the items that are in the user's cart for checkout.
 */
data class CartItems(
  val items: Set<Item>
)

/**
 * This ViewState encapsules all of our users and their items, as well as the cart information
 * so we know which items are inside the cart.
 */
data class ViewState(
  val usersAndItems: List<UserItems>,
  val cartItems: CartItems
)