滑动缩放 CenterZoomLinearLayoutManager

CenterZoomLinearLayoutManager

class CenterZoomLinearLayoutManager(context: Context)
    : LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false) {

    override fun onLayoutCompleted(state: RecyclerView.State?) {
        super.onLayoutCompleted(state)
        scaleChildren()
    }

    override fun scrollHorizontallyBy(dx: Int, recycler: RecyclerView.Recycler?, state: RecyclerView.State?): Int {
        return if (orientation == HORIZONTAL) {
            super.scrollHorizontallyBy(dx, recycler, state).also { scaleChildren() }
        } else {
            0
        }
    }

    /**
     * 参考 https://www.jianshu.com/p/198748de8581
     * https://stackoverflow.com/questions/32823713/how-to-scale-up-recycler-view-center-item-while-scrolling-in-android/54516315#54516315
     * 300/375
     */
    private fun scaleChildren() {
        val midpoint = width / 2f
        val d1 = 0.9f * midpoint
        for (i in 0 until childCount) {
            val child = getChildAt(i) as View
            val d = Math.min(d1, Math.abs(midpoint - (getDecoratedRight(child) + getDecoratedLeft(child)) / 2f))
            val scale = 1f - 0.1f * d / d1
            child.scaleY = scale
        }
    }
}