Databinding in recyclerView item doesn't work with the fragment viewModel

Question

I have a recyclerView that shows a list of cart items, Every item is clickable and opens details fragment for that item, I'm Updating the item layout to have a delete button inside, the delete button suppose to call a method inside the fragment viewModel. I believe that making the viewModel a constructor in the adapter is not the best practice since separation of concern is important as I develop my skills.

I'm doing so with dataBinding and I've searched so much and couldn't find an answer.

CartListItem.xml

CartAdapter

class CartAdapter(private val clickListener: (MakeupItem) -> Unit) :
ListAdapter(DiffCallback()) {

class CartViewHolder(private val binding: CartListItemBinding) :
    RecyclerView.ViewHolder(binding.root) {
    fun bind(makeupItem: MakeupItem) {
        binding.makeupItem = makeupItem
        binding.executePendingBindings()
    }
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CartViewHolder {
    val layoutInflater = LayoutInflater.from(parent.context)
    val binding = CartListItemBinding.inflate(layoutInflater, parent, false)
    return CartViewHolder(binding)
}

override fun onBindViewHolder(holder: CartViewHolder, position: Int) {
    val makeupItem = getItem(position)
    holder.itemView.setOnClickListener {
        clickListener(makeupItem)
    }
    holder.bind(makeupItem)
}

class DiffCallback : DiffUtil.ItemCallback() {
    override fun areItemsTheSame(oldItem: MakeupItem, newItem: MakeupItem): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: MakeupItem, newItem: MakeupItem): Boolean {
        return oldItem == newItem
    }
}

CartViewModel delete function

fun deleteItemFromCart(makeupItem: MakeupItem) {
    viewModelScope.launch {
        Log.d(TAG, "DeleteItemFromCart method in viewModel called")
        repository.deleteItemFromCart(makeupItem)
    }
}

Mahmoud Reda · Accepted Answer

I've came to an answer.

DataBinding of a viewModel with a recyclerView item won't work since we're not declaring the adapter in this viewModel, so you should make a callBack inside your adapter and receive it in your fragment then call your viewModel function.

Here is CartAdapter after modifying a callBack for your delete button onClick and use the same way for your cardItem

class CartAdapter(
private val cartItemClickListener: CartItemClickListener,
private val deleteItemClickListener: DeleteItemClickListener
) :
ListAdapter(DiffCallback()) {

class CartViewHolder(private val binding: CartListItemBinding) :
    RecyclerView.ViewHolder(binding.root) {
    fun bind(
        makeupItem: MakeupItem,
        cartItemClickListener: CartItemClickListener,
        deleteItemClickListener: DeleteItemClickListener
    ) {
        binding.makeupItem = makeupItem
        binding.cartItemClickListener = cartItemClickListener
        binding.deleteItemClickListener = deleteItemClickListener
        binding.executePendingBindings()
    }
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CartViewHolder {
    val layoutInflater = LayoutInflater.from(parent.context)
    val binding = CartListItemBinding.inflate(layoutInflater, parent, false)
    return CartViewHolder(binding)
}

override fun onBindViewHolder(holder: CartViewHolder, position: Int) {
    val makeupItem = getItem(position)
    holder.bind(makeupItem, cartItemClickListener, deleteItemClickListener)
}

class DiffCallback : DiffUtil.ItemCallback() {
    override fun areItemsTheSame(oldItem: MakeupItem, newItem: MakeupItem): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: MakeupItem, newItem: MakeupItem): Boolean {
        return oldItem == newItem
    }
}

class CartItemClickListener(val clickListener: (makeupItem: MakeupItem) -> Unit) {
    fun onClick(makeupItem: MakeupItem) = clickListener(makeupItem)
}

class DeleteItemClickListener(val deleteItemClickListener: (makeupItem: MakeupItem) -> Unit) {
    fun onClick(makeupItem: MakeupItem) = deleteItemClickListener(makeupItem)
}

}

As for CartListItem add two dataBinding one itemClickListener and the other for deleteButtonClickListener and use android:onClick and a lambda expression inside it

Once you get to your fragment and declaring your adapter pass the adapter parameters which will do a certain viewModel function or whatever you need to implement on every click of your cardItem and delete button

adapter = CartAdapter(CartAdapter.CartItemClickListener { makeupItem ->
        viewModel.onMakeupItemClicked(makeupItem)
    }, CartAdapter.DeleteItemClickListener { makeupItem ->
        viewModel.deleteItemFromCart(makeupItem)
    }
    )

I hope this is the best practice answer and helps everyone has the same issue.

Databinding in recyclerView item doesn't work with the fragment viewModel

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