Adjusting View Pager which adjusts its height according to the view's height in focus

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.aqua30.learningproject.AdjustingViewPager
            android:id="@+id/view_pager"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:layout_constraintTop_toTopOf="parent" />

        <ImageView
            android:id="@+id/iv_heart"
            android:layout_width="@dimen/width_action_icon"
            android:layout_height="@dimen/height_action_icon"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginTop="@dimen/margin_16"
            android:layout_marginStart="@dimen/margin_16"
            android:src="@drawable/ic_heart"
            app:layout_constraintTop_toBottomOf="@id/view_pager" />

        <ImageView
            android:id="@+id/iv_comment"
            android:layout_width="@dimen/width_action_icon"
            android:layout_height="@dimen/height_action_icon"
            android:src="@drawable/ic_comment"
            android:layout_marginStart="@dimen/margin_24"
            app:layout_constraintStart_toEndOf="@id/iv_heart"
            app:layout_constraintTop_toTopOf="@id/iv_heart" />

        <ImageView
            android:id="@+id/iv_share"
            android:layout_width="@dimen/width_action_icon"
            android:layout_height="@dimen/height_action_icon"
            android:src="@drawable/ic_share"
            android:layout_marginStart="@dimen/margin_24"
            app:layout_constraintStart_toEndOf="@id/iv_comment"
            app:layout_constraintTop_toTopOf="@id/iv_heart" />

        <TextView
            android:id="@+id/tv_actions_count"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:layout_constraintStart_toStartOf="@id/iv_heart"
            app:layout_constraintTop_toBottomOf="@id/iv_heart"
            android:layout_marginTop="@dimen/margin_16"
            android:text="@string/action_count"
            android:textColor="#95a5a6"
            android:textSize="@dimen/text_size_12" />

        <TextView
            android:id="@+id/tv_description"
            android:layout_width="0dp"
            android:layout_height="0dp"
            app:layout_constraintStart_toStartOf="@id/iv_heart"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toBottomOf="@id/tv_actions_count"
            app:layout_constraintBottom_toBottomOf="parent"
            android:layout_marginEnd="@dimen/margin_16"
            android:layout_marginTop="@dimen/margin_16"
            android:text="@string/description"
            android:textColor="#000000"
            android:textSize="@dimen/text_size_16" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</ScrollView>

AdjustingViewPager.kt

package com.aqua30.learningproject

import android.content.Context
import android.util.AttributeSet
import android.util.Log
import android.view.View
import android.view.View.MeasureSpec
import androidx.viewpager.widget.ViewPager

class AdjustingViewPager: ViewPager {

    private lateinit var currentView: View  /* current page view in focus */
    private val maxHeight= 480f /* maximum height that we want on screen */
    private val allowedHeight = convertDpToPixel(maxHeight) /* allowed height in pixel */

    constructor(context: Context) : super(context)
    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        var newViewHeight = heightMeasureSpec
        val mode = MeasureSpec.getMode(heightMeasureSpec)
        /* until the parent has not assigned the size to the view
           and it is either not determined or at its maximum, assign it
           the new measurement as it comes in focus
         */
        if (mode == MeasureSpec.UNSPECIFIED || mode == MeasureSpec.AT_MOST) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec)
            if (currentView == null) {
                super.onMeasure(widthMeasureSpec, heightMeasureSpec)
                return
            }
            try {
                /* measuring the current dimensions */
                currentView.measure(
                    widthMeasureSpec, MeasureSpec.makeMeasureSpec(
                        0,
                        MeasureSpec.UNSPECIFIED
                    )
                )
                var currentViewHeight = currentView.measuredHeight
                /*
                   if the current view height is greater than allowed height then
                   set it to allowed height
                */
                if (currentViewHeight > allowedHeight) {
                   currentViewHeight = allowedHeight.toInt()
                }
                newViewHeight = MeasureSpec.makeMeasureSpec(currentViewHeight, MeasureSpec.EXACTLY)
            } catch (e: NullPointerException) {
                Log.e(AdjustingViewPager::class.simpleName, ": " + e.message)
            }
        }
        super.onMeasure(widthMeasureSpec, newViewHeight)
    }

    fun measureCurrentView(view: View) {
        this.currentView = view
        requestLayout()
    }

    private fun convertDpToPixel(dp: Float): Float {
        val metrics = context.resources.displayMetrics
        return dp * (metrics.densityDpi / 160f)
    }
}

ImagePagerAdapter.kt

package com.aqua30.learningproject

import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import androidx.viewpager.widget.PagerAdapter
import com.bumptech.glide.Glide

class ImagePagerAdapter: PagerAdapter {

    var imagesList: List<Int>? = null
    var context: Context? = null
    var currentPosition = -1

    constructor(context: Context, imagesList: List<Int>): super() {
        this.imagesList = imagesList
        this.context = context
    }

    override fun getCount(): Int {
        return imagesList?.size!!
    }

    override fun isViewFromObject(view: View, `object`: Any): Boolean {
        return view == `object`
    }

    override fun instantiateItem(container: ViewGroup, position: Int): Any {
        val view = LayoutInflater.from(context).inflate(R.layout.view_item, container, false)
        val imageView: ImageView = view.findViewById(R.id.iv_item)
        container.addView(view)
        Glide.with(context!!)
            .load(imagesList?.get(position))
            .into(imageView)
        return view
    }

    override fun setPrimaryItem(container: ViewGroup, position: Int, `object`: Any) {
        super.setPrimaryItem(container, position, `object`)
        if (container !is AdjustingViewPager)
            return
        if (position != currentPosition) {
            val viewPager: AdjustingViewPager = container
            currentPosition = position;
            viewPager.measureCurrentView(`object` as View)
        }
    }

    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
        container.removeView(`object` as View)
    }
}

MainActivity.kt

package com.aqua30.learningproject

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    lateinit var viewPager : AdjustingViewPager
    lateinit var imageAdapter: ImagePagerAdapter
    private val imagesList: List<Int> = listOf(
        R.drawable.img_1,
        R.drawable.img_2,
        R.drawable.img_3
    )

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        viewPager = findViewById(R.id.view_pager)
        imageAdapter = ImagePagerAdapter(this, imagesList)
        viewPager.adapter = imageAdapter
    }
}

view_item.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:maxHeight="430dp">

    <ImageView
        android:id="@+id/iv_item"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</FrameLayout>

This code has clearly been auto-migrated from Java and has some issues:

1. AdjustingViewPager:28 - currentView cannot be null
2. the name object in ImagePagerAdapter
3. nullable vars in ImagePagerAdapter
4. isViewFromObject should compare the two things with ===

@kryanod This is not auto-migrated code from java. I wrote it in kotlin.
Let me know what issues you're facing.

For the point 1, are you calling viewPager.measureCurrentView(object as View) because otherwise you'll get currentView cannot be null

For point 2, as I'm learning kotlin so i used the defaults.

For point 3, please provide exact error you get.

Ah OK sorry, I misunderstood the whole thing then. Let me clarify my points though.
1 - your property is a lateinit var and has a type of View, i.e. it can never be null. This means that the null check at AdjustingViewPager:28 can never return true
3 - It's just a convenience thing. You can declare the whole class as

class ImagePagerAdapter(private val context: Context, private val imagesList: List<Int>)

and get rid of an extra constructor and the first two vars

Agreed @kryanod. Will update this.