A custom View Pager with some gestures and animations

CViewPager.kt

package eram.ir.camerapager

import android.animation.ValueAnimator
import android.app.Activity
import android.content.Context
import android.support.v4.app.FragmentActivity
import android.support.v4.view.ViewPager
import android.util.AttributeSet
import android.util.Log
import android.view.MotionEvent
import android.view.View
import android.view.ViewGroup
import android.view.animation.DecelerateInterpolator
import android.widget.Scroller


class CViewPager @JvmOverloads constructor(
        context: Context, attrs: AttributeSet? = null
) : ViewPager(context, attrs) {

    var enabledScroll = true
    lateinit var exitListener: ExitListener

    init {
        setMyScroller()
    }

    fun setOnExitListener(exitListener: ExitListener) {
        this.exitListener = exitListener
    }

    override fun onTouchEvent(ev: MotionEvent?): Boolean {
        return super.onTouchEvent(ev) && (onDrag(ev))
    }

    override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
        return if (enabledScroll) super.onInterceptTouchEvent(ev) else false
    }


    override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
        return super.dispatchTouchEvent(ev) && (onDrag(ev))
    }

    var startPointY = 0f
    var prevY = 0f
    var startPointX = 0f
    private fun onDrag(ev: MotionEvent?): Boolean {
        when (ev!!.action) {
            MotionEvent.ACTION_DOWN -> {
                prevY = getItemViewAt(currentItem).y
                startPointY = ev.rawY
                startPointX = ev.rawX

            }
            MotionEvent.ACTION_MOVE -> {
                Log.i("current child", (context as FragmentActivity).supportFragmentManager.findFragmentByTag("android:switcher:" + id + ":"
                        + currentItem)::class.java.canonicalName)
                if (ev.action == MotionEvent.ACTION_MOVE && !enabledScroll && ev.rawY - startPointY > 0) {
                    getItemViewAt(currentItem).y = ev.rawY - startPointY
                    return enabledScroll
                }
            }
            MotionEvent.ACTION_UP -> {

                if (::exitListener.isInitialized && !enabledScroll)
                    if (getItemViewAt(currentItem).y > ev.y / 3) {
                        animateToRelease()
                        exitListener.onExit()
                    } else {
                        animateToRelease()
                    }

                return (ev.x - startPointX) == 0f
            }

        }

        return true
    }

    private fun getItemViewAt(index: Int): View {
        val fragment = (context as FragmentActivity).supportFragmentManager.findFragmentByTag("android:switcher:" + id + ":"
                + currentItem)
        return fragment.view!!
    }

    private fun animateToRelease() {
        val animator = ValueAnimator.ofFloat(getItemViewAt(currentItem).y, prevY)
        animator.addUpdateListener { animation ->
            getItemViewAt(currentItem).y = animation.animatedValue as Float
        }
        animator.interpolator = DecelerateInterpolator()
        animator.duration = 500
        animator.start()

    }

    private fun setMyScroller() {
        try {
            val viewpager = ViewPager::class.java
            val scroller = viewpager.getDeclaredField("mScroller")
            scroller.isAccessible = true
            scroller.set(this, MyScroller(context))
        } catch (e: Exception) {
            e.printStackTrace()
        }

    }

    inner class MyScroller(context: Context) : Scroller(context, DecelerateInterpolator()) {

        override fun startScroll(startX: Int, startY: Int, dx: Int, dy: Int, duration: Int) {
            super.startScroll(startX, startY, dx, dy, if (enabledScroll) 200 else 500 /*1 secs*/)
        }
    }


    interface ExitListener {
        fun onExit()
    }
}