android kotlin - RecyclerView smooth scroll

MainActivity.kt


package com.cfsuman.kotlintutorials

import android.os.Bundle
import android.widget.Button
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView


class MainActivity : AppCompatActivity() {
    private lateinit var context:MainActivity

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Get the context
        context = this;

        // Get the widgets reference from XML layout
        val btnTop = findViewById<Button>(R.id.btnTop)
        val btnMiddle = findViewById<Button>(R.id.btnMiddle)
        val btnBottom = findViewById<Button>(R.id.btnBottom)
        val recyclerView = findViewById<RecyclerView>(R.id.recyclerView)


        // initialize a mutable list of animals
        val animals = mutableListOf(
            "Horse", "Donkey", "Goat",
            "Squirrel", "Mouse", "Chameleon",
            "Deer", "Raccoon", "Antelope",
            "Beaver", "Weasel", "Hedgehog",
            "Ferret", "Koala", "Wolf",
            "Lynx", "Groundhog", "Anteater",
            "Wombat"
        )

        // initialize an instance of linear layout manager
        val layoutManager = LinearLayoutManager(
            context, // context
            RecyclerView.VERTICAL, // orientation
            false // reverse layout
        ).apply {
            // specify the layout manager for recycler view
            recyclerView.layoutManager = this
        }

        // finally, data bind the recycler view with adapter
        val adapter = RecyclerViewAdapter(animals).apply {
            recyclerView.adapter = this
        }


        // smooth scroll to recycler view item position
        // smooth scroll to recycler view top
        btnTop.setOnClickListener {
            recyclerView.smoothScrollToPosition(0)
        }

        // smooth scroll to recycler view middle item
        btnMiddle.setOnClickListener {
            recyclerView.smoothScrollToPosition(
                adapter.itemCount/2)
        }

        // smooth scroll to recycler view bottom
        btnBottom.setOnClickListener {
            recyclerView.smoothScrollToPosition(
                adapter.itemCount-1)
        }
    }
}

RecyclerViewAdapter.kt


package com.cfsuman.kotlintutorials

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView


class RecyclerViewAdapter(private val animals: MutableList<String>)
    : RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder>() {

    override fun onCreateViewHolder(
        parent: ViewGroup, viewType: Int): ViewHolder {
        // inflate the custom view from xml layout file
        val view: View = LayoutInflater.from(parent.context)
            .inflate(R.layout.custom_view,parent,false)

        // return the view holder
        return ViewHolder(view)
    }


    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        // display the current animal
        holder.animal.text = "${position+1}. ${animals[position]}"
    }


    override fun getItemCount(): Int {
        // number of items in the data set held by the adapter
        return animals.size
    }


    class ViewHolder(itemView: View)
        : RecyclerView.ViewHolder(itemView){
        val animal: TextView = itemView.findViewById(R.id.tvAnimal)
    }


    // this two methods useful for avoiding duplicate item
    override fun getItemId(position: Int): Long {
        return position.toLong()
    }


    override fun getItemViewType(position: Int): Int {
        return position
    }
}

activity_main.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/rootLayout"
    android:background="#DCDCDC"
    android:padding="8dp">

    <Button
        android:id="@+id/btnTop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Top"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnMiddle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Middle"
        app:layout_constraintBottom_toBottomOf="@+id/btnTop"
        app:layout_constraintStart_toEndOf="@+id/btnTop" />

    <Button
        android:id="@+id/btnBottom"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Bottom"
        app:layout_constraintBottom_toBottomOf="@+id/btnMiddle"
        app:layout_constraintStart_toEndOf="@+id/btnMiddle" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnTop" />

</androidx.constraintlayout.widget.ConstraintLayout>

custom_view.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/cardView"
    android:layout_width="match_parent"
    android:layout_height="125dp"
    app:cardBackgroundColor="#F8F8F8"
    app:cardCornerRadius="8dp"
    app:cardElevation="4dp"
    app:cardMaxElevation="6dp"
    app:contentPadding="24dp"
    android:layout_margin="4dp">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:id="@+id/tvAnimal"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:fontFamily="sans-serif"
            android:gravity="center"
            android:textSize="22sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>

</androidx.cardview.widget.CardView>