RecyclerView で区切り線引きたくなったら書くクラス

DividerItemDecoration.kt

package Util

import android.R
import android.content.Context
import android.graphics.Canvas
import android.graphics.Rect
import android.graphics.drawable.Drawable
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.View

/**
 * RecyclerView に区切り線を提供します
 */
class DividerItemDecoration(context: Context, orientation: Int) : RecyclerView.ItemDecoration() {
    private val attrs: IntArray by lazy { intArrayOf(R.attr.listDivider) }
    private val mDivider: Drawable by lazy { context.obtainStyledAttributes(this.attrs).getDrawable(0) }
    private var mOrientation: Int = 0

    init {
        val a = context.obtainStyledAttributes(this.attrs)
        a.recycle()
        setOrientation(orientation)
    }

    /**
     * orientation の値を設定します
     */
    fun setOrientation(orientation: Int) {
        if (orientation != LinearLayoutManager.HORIZONTAL && orientation != LinearLayoutManager.VERTICAL) {
            throw IllegalArgumentException("invalid orientation")
        }
        this.mOrientation = orientation
    }

    /**
     * 区切り線の描画を行います
     */
    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State): Unit
            = if (this.mOrientation == LinearLayoutManager.VERTICAL) drawVertical(c, parent) else drawHorizontal(c, parent)

    /**
     * vertical 方向に区切り線を描画します
     */
    fun drawVertical(c: Canvas, parent: RecyclerView): Unit {
        val left = parent.paddingLeft
        val right = parent.width - parent.paddingRight

        val childCount = parent.childCount
        for (i in 0..childCount - 1) {
            val child = parent.getChildAt(i)
            val params = child.layoutParams as RecyclerView.LayoutParams
            val top = child.bottom + params.bottomMargin
            val bottom = top + this.mDivider.intrinsicHeight
            this.mDivider.setBounds(left, top, right, bottom)
            this.mDivider.draw(c)
        }
    }

    /**
     * horizontal 方向に区切り線を描画します
     */
    fun drawHorizontal(c: Canvas, parent: RecyclerView) {
        val top = parent.paddingTop
        val bottom = parent.height - parent.paddingBottom

        val childCount = parent.childCount
        for (i in 0..childCount - 1) {
            val child = parent.getChildAt(i)
            val params = child.layoutParams as RecyclerView.LayoutParams
            val left = child.right + params.rightMargin
            val right = left + this.mDivider.intrinsicHeight
            this.mDivider.setBounds(left, top, right, bottom)
            this.mDivider.draw(c)
        }
    }

    /**
     * 描画された水平線の上下左右のオフセットを設定します
     */
    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State)
            = if (this.mOrientation == LinearLayoutManager.VERTICAL) outRect.set(0, 0, 0, this.mDivider.intrinsicHeight) else outRect.set(0, 0, this.mDivider.intrinsicWidth, 0)
}