Create Custom Intro Slider of an Android App with Kotlin

package com.gtappdevelopers.kotlingfgproject

data class SliderData(
    // on below line we are creating a string 
    // for our slide title, slide
    // description and image.
    var slideTitle: String,
    var slideDescription: String,
    var slideImage: Int
)

package com.gtappdevelopers.kotlingfgproject

import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.RelativeLayout
import android.widget.TextView
import androidx.viewpager.widget.PagerAdapter

class SliderAdapter(
    val context: Context,
    val sliderList: ArrayList<SliderData>
) : PagerAdapter() {

    override fun getCount(): Int {
        // on below line we are returning
        // the size of slider list
        return sliderList.size
    }

    override fun isViewFromObject(view: View, `object`: Any): Boolean {
        // inside isViewFromobject method we are
        // returning our Relative layout object.
        // inside isViewFromobject method we are
        // returning our Relative layout object.
        return view === `object` as RelativeLayout
    }

    override fun instantiateItem(container: ViewGroup, position: Int): Any {
        // in this method we will initialize all our layout
        // items and inflate our layout file as well.
        // in this method we will initialize all our layout
        // items and inflate our layout file as well.
        val layoutInflater: LayoutInflater =
            context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater

        // below line is use to inflate the
        // layout file which we created.

        // below line is use to inflate the
        // layout file which we created.
        val view: View = layoutInflater.inflate(R.layout.slider_item, container, false)

        // on below line we are initializing our image view, 
        // heading text view and description text view with their ids.
        val imageView: ImageView = view.findViewById(R.id.idIVSlider)
        val sliderHeadingTV: TextView = view.findViewById(R.id.idTVSliderTitle)
        val sliderDescTV: TextView = view.findViewById(R.id.idTVSliderDescription)

        // on below line we are setting data to our text view 
        // and image view on below line.
        val sliderData: SliderData = sliderList.get(position)
        sliderHeadingTV.text = sliderData.slideTitle
        sliderDescTV.text = sliderData.slideDescription
        imageView.setImageResource(sliderData.slideImage)
        
        // on below line we are adding our view to container.
        container.addView(view)

        // on below line we are returning our view.
        return view
    }

    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
        // this is a destroy view method
        // which is use to remove a view.
        // this is a destroy view method
        // which is use to remove a view.
        container.removeView(`object` as RelativeLayout)
    }

}

package com.gtappdevelopers.kotlingfgproject

import android.content.Intent
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.viewpager.widget.ViewPager

class MainActivity : AppCompatActivity() {

    // on below line we are creating a 
    // variable for our view pager
    lateinit var viewPager: ViewPager

    // on below line we are creating a variable
    // for our slider adapter and slider list
    lateinit var sliderAdapter: SliderAdapter
    lateinit var sliderList: ArrayList<SliderData>

    // on below line we are creating a variable for our 
    // skip button, slider indicator text view for 3 dots
    lateinit var skipBtn: Button
    lateinit var indicatorSlideOneTV: TextView
    lateinit var indicatorSlideTwoTV: TextView
    lateinit var indicatorSlideThreeTV: TextView

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

        // on below line we are initializing all 
        // our variables with their ids.
        viewPager = findViewById(R.id.idViewPager)
        skipBtn = findViewById(R.id.idBtnSkip)
        indicatorSlideOneTV = findViewById(R.id.idTVSlideOne)
        indicatorSlideTwoTV = findViewById(R.id.idTVSlideTwo)
        indicatorSlideThreeTV = findViewById(R.id.idTVSlideThree)

        // on below line we are adding click listener for our skip button
        skipBtn.setOnClickListener {
            // on below line we are opening a new activity
            val i = Intent(this@MainActivity, MainActivity2::class.java)
            startActivity(i)
        }

        // on below line we are initializing our slider list.
        sliderList = ArrayList()

        // on below line we are adding data to our list
        sliderList.add(
            SliderData(
                "Python",
                "Python Development Course",
                R.drawable.python
            )
        )

        sliderList.add(
            SliderData(
                "Java",
                "Java Development Course",
                R.drawable.java
            )
        )

        sliderList.add(
            SliderData(
                "C++",
                "C++ Development Course",
                R.drawable.c
            )
        )

        // on below line we are adding slider list
        // to our adapter class.
        sliderAdapter = SliderAdapter(this, sliderList)

        // on below line we are setting adapter 
        // for our view pager on below line.
        viewPager.adapter = sliderAdapter

        // on below line we are adding page change 
        // listener for our view pager.
        viewPager.addOnPageChangeListener(viewListener)

    }

    // creating a method for view pager for on page change listener.
    var viewListener: ViewPager.OnPageChangeListener = object : ViewPager.OnPageChangeListener {
        override fun onPageScrolled(
            position: Int,
            positionOffset: Float,
            positionOffsetPixels: Int
        ) {
        }

        override fun onPageSelected(position: Int) {
            // we are calling our dots method to
            // change the position of selected dots.

            // on below line we are checking position and updating text view text color.
            if (position == 0) {
                indicatorSlideTwoTV.setTextColor(resources.getColor(R.color.grey))
                indicatorSlideThreeTV.setTextColor(resources.getColor(R.color.grey))
                indicatorSlideOneTV.setTextColor(resources.getColor(R.color.white))

            } else if (position == 1) {
                indicatorSlideTwoTV.setTextColor(resources.getColor(R.color.white))
                indicatorSlideThreeTV.setTextColor(resources.getColor(R.color.grey))
                indicatorSlideOneTV.setTextColor(resources.getColor(R.color.grey))
            } else {
                indicatorSlideTwoTV.setTextColor(resources.getColor(R.color.grey))
                indicatorSlideThreeTV.setTextColor(resources.getColor(R.color.white))
                indicatorSlideOneTV.setTextColor(resources.getColor(R.color.grey))
            }
        }

        // below method is use to check scroll state.
        override fun onPageScrollStateChanged(state: Int) {}
    }
}