A simple yet fully featured RecyclerView ItemDecorator that draws a divider line between items. Only works with vertical LinearLayoutManagers!

DividerItemDecorator.kt

package me.seebrock3r.common.widget

import android.graphics.Canvas
import android.graphics.Paint
import android.graphics.Rect
import android.view.View
import androidx.annotation.ColorInt
import androidx.annotation.Px
import androidx.core.graphics.withTranslation
import androidx.core.view.children
import androidx.recyclerview.widget.RecyclerView

class DividerItemDecorator(
    @param:ColorInt @field:ColorInt private val strokeColor: Int,
    @param:Px @field:Px private val strokeWidth: Int,
    @param:Px @field:Px private val marginStart: Float = 0.0F,
    @param:Px @field:Px private val marginEnd: Float = marginStart,
    @param:Px @field:Px private val horizontalSpacing: Int,
    @param:Px @field:Px private val verticalSpacing: Int = horizontalSpacing
) : RecyclerView.ItemDecoration() {

    private val dividerPaint = Paint().apply {
        color = strokeColor
        flags = Paint.ANTI_ALIAS_FLAG
    }

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
        outRect.set(horizontalSpacing, verticalSpacing, horizontalSpacing, verticalSpacing)
    }

    override fun onDrawOver(canvas: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        parent.children.forEach { child ->
            if (child.isNotLastItem(parent, state.itemCount))
                canvas.withTranslation(x = 0.0F, y = verticalSpacing.toFloat()) {
                    val lineY = child.bottom - strokeWidth / 2.0F
                    drawLine(
                        child.left + marginStart,
                        lineY,
                        child.right - marginEnd,
                        lineY,
                        dividerPaint
                    )
                }
        }
    }

    private fun View.isNotLastItem(parent: RecyclerView, itemCount: Int) =
        parent.getChildAdapterPosition(this) < itemCount - 1
}