[FIXED] RecyclerView itemClickListener in Kotlin

Issue

I'm writing my first app in Kotlin after 3 years of experience with Android. Just confused as to how to utilize itemClickListener with a RecyclerView in Kotlin.

I have tried the trait (edit: now interface) approach, very Java-like

public class MainActivity : ActionBarActivity() {

  protected override fun onCreate(savedInstanceState: Bundle?) {

    // set content view etc go above this line

    class itemClickListener : ItemClickListener {
      override fun onItemClick(view: View, position: Int) {
        Toast.makeText(this@MainActivity, "TEST: " + position, Toast.LENGTH_SHORT).show()
      }
    }

    val adapter = DrawerAdapter(itemClickListener())
    mRecyclerView.setAdapter(adapter)
 }

  trait ItemClickListener {
    fun onItemClick(view: View, position: Int)
  }
}

That seemed very redundant so I tried the inner class approach:

inner class ItemClickListener {
    fun onItemClick(view: View, position: Int) {
        startActivityFromFragmentForResult<SelectExerciseActivity>(SELECT_EXERCISES)
    }
}

And then just setting the adapter's click listener like this:

val adapter = WorkoutsAdapter(ItemClickListener())

But I'm still not satisfied with this because I think there might be a better, cleaner way. I'm trying to essentially achieve something like this: RecyclerView onClick

Any suggestions?

Ended up going with a variation of the approved answer

Defined the function in the activity:

val itemOnClick: (View, Int, Int) -> Unit = { view, position, type ->
    Log.d(TAG, "test")
}

Passed the function itself on to the adapter like this:

class ExercisesAdapter(val itemClickListener: (View, Int, Int) -> Unit) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
      // other stuff up here
      val vhExercise = ExerciseVH(view) // view holder
      // on to the view holder through the extension function
      vhExercise.onClick(itemClickListener)
    }
}

Extension function by Loop in the approved answer below.

fun <T : RecyclerView.ViewHolder> T.onClick(event: (view: View, position: Int, type: Int) -> Unit): T {
    itemView.setOnClickListener {
        event.invoke(it, getAdapterPosition(), getItemViewType())
    }
    return this
}

Solution

I have a little bit different approach. You can create an extension for your ViewHolder

fun <T : RecyclerView.ViewHolder> T.listen(event: (position: Int, type: Int) -> Unit): T {
    itemView.setOnClickListener {
        event.invoke(getAdapterPosition(), getItemViewType())
    }
    return this
}

Then use it in adapter like this

class MyAdapter : RecyclerView.Adapter<MyAdapter.MyViewHolder>() {

    val items: MutableList<String> = arrayListOf()

    override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): MyViewHolder? {
        val inflater = LayoutInflater.from(parent!!.getContext())
        val view = inflater.inflate(R.layout.item_view, parent, false)
        return MyViewHolder(view).listen { pos, type ->
            val item = items.get(pos)
            //TODO do other stuff here
        }
    }

    override fun onBindViewHolder(holder: MyViewHolder?, position: Int) {

    }

    override fun getItemCount(): Int {
        return items.size()
    }


    class MyViewHolder(view: View) : RecyclerView.ViewHolder(view) {

    }
}

I am working with my colleagues on library providing such extensions.

Answered By - Damian Petla
Answer Checked By - Robin (JavaFixing Admin)