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
}

This is great! thanks for sharing!
I would slightly change some small details:

• move state.itemCount out the loop to avoid calling this method all the time.
• substract 1 to itemCount to ignore last item
• do a forEachIndexed to avoid calling parent.getChildAdapterPosition(this)

    override fun onDrawOver(canvas: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        val itemCount = state.itemCount - 1 // this is to ignore last item
        parent.forEachIndexed { index, child ->
            if (index < 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
                    )
                }
            }
        }
    }

Please let me know your thoughts and thanks again!

How did you call forEachIndexed from the RecyclerView ? Cause this is not a collection