TopScrollLinearLayoutManager.kt

package com.mercadoni.user.android.faq

import android.content.Context
import android.graphics.PointF
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.LinearSmoothScroller
import android.support.v7.widget.RecyclerView
import android.util.DisplayMetrics

/**
 *
 */
class TopScrollLinearLayoutManager(context: Context) : LinearLayoutManager(context) {

    companion object {

        const val MILLISECONDS_PER_INCH = 50f

    }

    override fun smoothScrollToPosition(recyclerView: RecyclerView, state: RecyclerView.State?,
                                        position: Int) {
        val smoothScroller = TopSnappedSmoothScroller(recyclerView.context)
        smoothScroller.targetPosition = position
        startSmoothScroll(smoothScroller)
    }

    private inner class TopSnappedSmoothScroller(context: Context) : LinearSmoothScroller(context) {

        override fun computeScrollVectorForPosition(targetPosition: Int): PointF? {
            return this@TopScrollLinearLayoutManager
                    .computeScrollVectorForPosition(targetPosition)
        }

        override fun getVerticalSnapPreference(): Int {
            return SNAP_TO_START
        }

        override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics?): Float {
            if (displayMetrics == null) return super.calculateSpeedPerPixel(displayMetrics)
            else return MILLISECONDS_PER_INCH / displayMetrics.densityDpi
        }

    }

}