Simple Custom Linear Layout Manager

SimpleLinearLayoutManager.kt

import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.RecyclerView.Recycler
import java.lang.Integer.max
import java.lang.Integer.min

class HamidGridLayoutManager: RecyclerView.LayoutManager() {

    var offset = 0

    override fun generateDefaultLayoutParams(): RecyclerView.LayoutParams {
        return RecyclerView.LayoutParams(
            RecyclerView.LayoutParams.WRAP_CONTENT,
            RecyclerView.LayoutParams.WRAP_CONTENT
        )
    }

    override fun onLayoutChildren(recycler: RecyclerView.Recycler, state: RecyclerView.State?) {
        fill(recycler)
    }

    private fun fill(recycler: Recycler) {
        if (itemCount == 0) return
        detachAndScrapAttachedViews(recycler)
        for (position in 0 until itemCount) {
            val view = recycler.getViewForPosition(position)
            addView(view)

            val layoutParams = view.layoutParams as RecyclerView.LayoutParams
            layoutParams.width = width
            layoutParams.height = width
            view.layoutParams = layoutParams

            var left = 0
            var right = left + width
            var top = position * width - offset
            var bottom = top + width
            measureChild(view, width, width)
            layoutDecorated(view, left, top, right, bottom)
        }
        val scrapListCopy = recycler.scrapList.toList()
        scrapListCopy.forEach {
            recycler.recycleView(it.itemView)
        }
    }

    override fun canScrollVertically(): Boolean {
        return true
    }

    override fun scrollVerticallyBy(
        dy: Int,
        recycler: Recycler?,
        state: RecyclerView.State?
    ): Int {
        if (itemCount == 0) return 0
        val lastOffset = offset
        val firstItem = requireNotNull(getChildAt(0))
        val lastItem = requireNotNull(getChildAt(itemCount - 1))
        val startOfFirstItem = getDecoratedTop(firstItem)
        val endOfLastItem = getDecoratedBottom(lastItem)
        offset = min(max(startOfFirstItem, offset + dy), offset + endOfLastItem - height)
        return lastOffset - offset
    }

}