Setting the OnClickListener on the list item is a very common task in Android development. As an Android developer, you should be well-familiar with it. However, I have seen various implementations from different developers. Back in the day when I still used Java, I would need an interface that specified the click listener’s behavior to handle the click action in the Fragment or Activity with the data from a specific item of the RecyclerView. The interface might look like this:
public interface OnItemClickListener {
void onItemClick(Model model);
}
Now in 2020, we have Kotlin and we can just use Lambda to achieve the same behavior as having the interface class in Java.
Let's begin with the RecyclerAdapter. In our Recycler Adapter, the constructor takes a Lambda as the constructor param. This Lambda acts as the listener with the model to be rendered in our Fragment/Activity.
class AwesomeAdapter(
private val onItemClicked: (Model) -> Unit
) : RecyclerView.Adapter<ViewHolder> {
var data: List<Model> = ArrayList(0)
set(value) {
field = value
notifyDataSetChanged()
}
}
Here comes the part where I have seen people implement it differently. Where do you think we should set the click listener to each item of the RecyclerView; onBindViewHolder or onCreateViewHolder?
Setting the click listener in onBindViewHolder is easy because the adapter is holding the list and we can access data items by their position in onBindViewHolder directly:
override fun onBindViewHolder(
holder: ViewHolder,
position: Int
) {
val item = data[position]
holder.bind(item)
holder.itemView.setOnClickListener { onItemClicked(item) }
}
}
However, in RecyclerView the onBindViewHolder gets called every time the ViewHolder is bound and the setOnClickListener will be triggered too. Therefore, setting a click listener in onCreateViewHolder which invokes only when a ViewHolder gets created is preferable.
Here is a diagram of the implementation.
In the Adapter class, onCreateViewHolder has no reference to the position, so we need to refer to RecyclerView item's position by the adapterPosition field in ViewHolder class. As you can see, we pass another Lambda into the ViewHolder class so that we can refer to an adapter position data in the Adapter class.
On Fragment/Activity
This is how we initialize the adapter with a click listener.
val adapter = AlbumAdapter {model ->
//The click action you want to perform.
}
On Adapter class
class ArtistAdapter(
private val onItemClicked: (Model) -> Unit
) : RecyclerView.Adapter<ArtistViewHolder>() {
var data: List<Model> = ArrayList(0)
set(value) {
field = value
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, type: Int): ArtistViewHolder {
val viewHolder = LayoutInflater.from(parent.context).inflate(R.layout.viewholder_awesome, parent, false)
return AwesomeViewHolder(viewHolder) {
onItemClick(values[it])
}
}
override fun getItemCount(): Int = data.size
override fun onBindViewHolder(viewHolder: ArtistViewHolder, position: Int) {
viewHolder.bind(data[position])
}
}
ViewHolder Class
class ArtistViewHolder(
view: View,
onItemClicked: (Int) -> Unit
) : RecyclerView.ViewHolder(view) {
init {
itemView.setOnClickListener {
onItemClicked(adapterPosition)
}
}
fun bind(model: Model) {
//bind data
}
}
Conclusion
I think setting a click listener of the RecyclerView item in onCreateViewHolder is a best practice since it reduces the function call significantly compared to doing it in onBindViewHolder. However, you might wonder if it is really necessary because setting a click listener is just a small operation and won't cause much of the performance issue anyway. That is true, but let's consider the situation where each item of the RecyclerView is getting more complex like having multiple click actions or even including a long click event. In this case, implementing the approach, I mentioned in this article would be more preferable.
And that is it! Thank you for reading.
Source
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was there a link to a sample implementation?
just trying to implement your idea now, and having a couple of little glitches.
thank you,
K
https://github.com/BenBoonya/android-pokemon-info/blob/master/app/src/main/java/com/benboonya/pokemoninfo/common/ui/PagedItemListAdapter.kt
onItemClick(values[it])
But shouldn't it read:
onItemClick(data[it])