RecyclerView通用分割线

class SimpleDividerItemDecoration : RecyclerView.ItemDecoration() {
    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        if (mSpanCount > 0) {  //表示GridLayoutManager  ||  StaggeredGridLayoutManager
            drawHorizontal(c, parent)
            drawVertical(c, parent)
        } else {  //表示LinearLayoutManager
            if (isVertical) {
                drawHorizontal(c, parent)
            } else {
                drawVertical(c, parent)
            }
        }
    }

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
        when (parent.layoutManager) {
            is StaggeredGridLayoutManager -> {
                (parent.layoutManager as StaggeredGridLayoutManager).apply {
                    mSpanCount = spanCount
                    outRect.set(0, 0, mDividerHeight, mDividerHeight)
                }
            }
            is GridLayoutManager -> {
                (parent.layoutManager as GridLayoutManager).apply {
                    mSpanCount = spanCount
                    outRect.set(0, 0, mDividerHeight, mDividerHeight)
                }
            }
            is LinearLayoutManager -> {
                if ((parent.layoutManager as LinearLayoutManager).orientation == LinearLayout.VERTICAL) {
                    outRect.set(0, 0, 0, mDividerHeight)
                } else {
                    outRect.set(0, 0, mDividerHeight, 0)
                    isVertical = false
                }
                mSpanCount = 0
            }
        }
    }

    private fun drawVertical(c: Canvas, parent: RecyclerView) {
        // -1表示忽略最后一个item
        for (i in 0 until parent.childCount - 1) {
            val child = parent.getChildAt(i)
            var left = child.right
            if (mSpanCount == 0) {
                // 让分割线充满RecyclerView
                left += parent.paddingRight
            }
            mDivider?.setBounds(left, child.top, left + mDividerHeight, child.bottom)
            mDivider?.draw(c)
        }
    }

    private fun drawHorizontal(c: Canvas, parent: RecyclerView) {
        // -1表示忽略最后一个item
        for (i in 0 until parent.childCount - 1) {
            val child = parent.getChildAt(i)
            val top = child.bottom
            var left = child.left
            var right = child.right
            if (mSpanCount == 0) {
                // 让分割线充满RecyclerView
                left -= parent.paddingLeft
                right += parent.paddingRight
            }
            mDivider?.setBounds(left, top, right, top + mDividerHeight)
            mDivider?.draw(c)
        }
    }
}