Recyclerview Card Item Onclick Kotlin

Question

I want to create a new intent/activity when the user clicks on a cardview respectively and i was wondering how does one do it in kotlin. i noticed most tutorials are in java and i'm a student who did not learn java.

package com.example.ttshfypj.adapters

import androidx.fragment.app.Fragment
import android.view.View
import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.example.ttshfypj.data_class.medications
import android.widget.ImageView
import android.widget.TextView
import com.example.ttshfypj.R

import com.squareup.picasso.Picasso
import kotlinx.android.synthetic.main.list_medication.view.*

class medicationAdapter (val medicationlist: ArrayList<medications>) : RecyclerView.Adapter<medicationAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val v = LayoutInflater.from(parent.context).inflate(R.layout.list_medication, parent, false)
        return ViewHolder(v)
    }

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

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val medicationgroup: medications = medicationlist[position]
        holder?.medicationnamevar?.text = medicationgroup.medicineN
        holder?.medicationschedulevar?.text = medicationgroup.MedicineTime
        val imagemedicine = holder?.itemView?.medicationimageview
        Picasso.get().load(medicationgroup.MedicineImage).into(imagemedicine)

    }
    class ViewHolder(itemView: View) :RecyclerView.ViewHolder(itemView) {
        val medicationnamevar = itemView.findViewById(R.id.medicationname) as TextView
        val medicationschedulevar = itemView.findViewById(R.id.medicationschedule) as TextView
    }




}

Answer 1

You can create an interface for Item Click Listener like

interface MyItemClickListener{
    fun itemClick(position: Int)
}

Now you should pass context to the constructor of your adapter.

class medicationAdapter (val medicationlist: ArrayList<medications>, var context: Context) : RecyclerView.Adapter<medicationAdapter.ViewHolder>() {...}

and create an instance of MyItemClickListener inside your adapter

// create instance of MyItemClickListener
private val clickListener = context as MyItemClickListener

And setclick listener on your view inside the onCreateViewHolder.

modify your adapter like this

class medicationAdapter (val medicationlist: ArrayList<medications>, var context: Context) : RecyclerView.Adapter<medicationAdapter.ViewHolder>() {

    // create instance of MyItemClickListener
    private val clickListener = context as MyItemClickListener

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {

        var inflater = LayoutInflater.from(parent.context)
        var v = inflater.inflate(R.layout.list_medication, parent, false)

        var viewHolder = ViewHolder(v)

        // here you set click listener on your item view.
        v.setOnClickListener {
            clickListener.itemClick(viewHolder.adapterPosition)
        }
        return viewHolder
    }

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

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val medicationgroup: medications = medicationlist[position]
        holder?.medicationnamevar?.text = medicationgroup.medicineN
        holder?.medicationschedulevar?.text = medicationgroup.MedicineTime
        val imagemedicine = holder?.itemView?.medicationimageview
        Picasso.get().load(medicationgroup.MedicineImage).into(imagemedicine)

    }
    class ViewHolder(itemView: View) :RecyclerView.ViewHolder(itemView) {
        val medicationnamevar = itemView.findViewById(R.id.medicationname) as TextView
        val medicationschedulevar = itemView.findViewById(R.id.medicationschedule) as TextView
    }
}

And finally, in your activity, you have to implement the MyItemClickListener interface and override the itemClick() like this

class YourActivity: AppCompatActivity(), MyItemClickListener {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // ....
   }

    override fun itemClick(position: Int) {
        Log.d("TAG","Click Item Position: "+position)
        // here you can call your new activity according to your item position.
    }
}

Answer 2

If you are using kotlin you can also use method reference where you directly pass a method to be called inside the adapter and you can directly invoke it there.

Activity.kt

Adapter(this::itemClickHandler);

private fun itemClickHandler(int position){
// your logic here
}

Adapter.kt

class Adapater(val itemClickHandler:(Int)->Unit):RecyclerView.Adapter(){

   override fun onBindViewHolder(){
      //you can invoke it here like this
     itemClickHandler.invoke(adapterPosition);
    } 

}

please refer this full code

MainActivity.kt

package com.example.myapplication

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import androidx.recyclerview.widget.LinearLayoutManager
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val list = mutableListOf<Items>()
        for(i in 1..25){
            list.add(Items(CHILD,"Child"))
        }
        with(rvList) {
            layoutManager = LinearLayoutManager(this@MainActivity)
            adapter = Adapter(list, this@MainActivity::onItemClickHandler)
        }

    }

     private fun onItemClickHandler(position:Int){
         Log.d("***","${position}");
        //here you can start a new intent to open a new activity on click of item

    }
}

The adapter code is as following

package com.example.myapplication

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import kotlinx.android.synthetic.main.layout_child.view.*
import kotlinx.android.synthetic.main.layout_header.view.*

const val HEADER = 1;
const val CHILD = 2;

data class Items(val type: Int, val text: String)

class Adapter(private val list: List<Items>, val itemClickHandler: (Int) -> Unit) :
    RecyclerView.Adapter<Adapter.HeaderViewHolder>() {


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): HeaderViewHolder {
        val headerView =
            LayoutInflater.from(parent.context).inflate(R.layout.layout_header, parent, false)
        val headerViewHolder = HeaderViewHolder(headerView)
        headerView.setOnClickListener {
            itemClickHandler.invoke(headerViewHolder.adapterPosition)
        }
        return headerViewHolder
    }

    override fun getItemCount(): Int = list.size

    override fun onBindViewHolder(holder: HeaderViewHolder, position: Int) {
        holder.onBind(list[position].text)

    }

    inner class HeaderViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        fun onBind(text: String) {
            itemView.tvHeader.text = text
        }
    }


}

Hope this helps and you are able to follow