This decorator adds equal spacing for items in GridLayoutManager

EqualSpaceItemDecoration.kt

package com.yourcompany.name

import android.graphics.Rect
import android.view.View
import androidx.recyclerview.widget.GridLayoutManager
import androidx.recyclerview.widget.RecyclerView

class EqualSpaceItemDecoration(private val padding: Int) :
    RecyclerView.ItemDecoration() {

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

        val layoutParams = view.layoutParams as GridLayoutManager.LayoutParams
        val gridLayoutManager = parent.layoutManager as? GridLayoutManager

        val spanSize = layoutParams.spanSize.toFloat()
        val totalSpanSize = gridLayoutManager!!.spanCount.toFloat()

        val n = totalSpanSize / spanSize // num columns
        val c = layoutParams.spanIndex / spanSize // column index

        val leftPadding = padding * ((n - c) / n)
        val rightPadding = padding * ((c + 1) / n)

        outRect.left = leftPadding.toInt()
        outRect.right = rightPadding.toInt()
        outRect.bottom = padding
    }
}