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()
    }
}

Custom View Pager with some gestures and animations