Created
January 8, 2023 14:23
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RecyclerView Custom LayoutManager to centrally zoom items.
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| class CenterZoomLayoutManager : LinearLayoutManager { | |
| private var mShrinkAmount = 0.1f | |
| private val mShrinkDistance = 0.9f | |
| constructor(context: Context?, orientation: Int, reverseLayout: Boolean, shrinkAmount: Float) : super( | |
| context, | |
| orientation, | |
| reverseLayout | |
| ) { | |
| mShrinkAmount = shrinkAmount | |
| } | |
| override fun generateDefaultLayoutParams(): RecyclerView.LayoutParams { | |
| return RecyclerView.LayoutParams( | |
| ViewGroup.LayoutParams.WRAP_CONTENT, | |
| ViewGroup.LayoutParams.WRAP_CONTENT | |
| ) | |
| } | |
| override fun canScrollHorizontally(): Boolean { | |
| return true | |
| } | |
| override fun scrollHorizontallyBy(dx: Int, recycler: Recycler, state: RecyclerView.State): Int { | |
| val orientation = orientation | |
| return if (orientation == HORIZONTAL) { | |
| val scrolled = super.scrollHorizontallyBy(dx, recycler, state) | |
| val midpoint = width / 2f | |
| val d0 = 0f | |
| val d1 = mShrinkDistance * midpoint | |
| val s0 = 1f | |
| val s1 = 1f - mShrinkAmount | |
| for (i in 0 until childCount) { | |
| val child = getChildAt(i) | |
| val childMidpoint = (getDecoratedRight(child!!) + getDecoratedLeft( | |
| child | |
| )) / 2f | |
| val d = min(d1, abs(midpoint - childMidpoint)) | |
| val scale = s0 + (s1 - s0) * (d - d0) / (d1 - d0) | |
| child.scaleX = scale | |
| child.scaleY = scale | |
| } | |
| scrolled | |
| } else { | |
| 0 | |
| } | |
| } | |
| override fun smoothScrollToPosition( | |
| recyclerView: RecyclerView, | |
| state: RecyclerView.State, | |
| position: Int | |
| ) { | |
| val linearSmoothScroller: LinearSmoothScroller = | |
| object : LinearSmoothScroller(recyclerView.context) { | |
| override fun computeScrollVectorForPosition(targetPosition: Int): PointF? { | |
| // Calculate the scroll vector for the target position | |
| return super.computeScrollVectorForPosition(targetPosition) | |
| } | |
| override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float { | |
| // Calculate the speed at which the RecyclerView should scroll | |
| return 0.1f / displayMetrics.densityDpi | |
| } | |
| } | |
| linearSmoothScroller.targetPosition = position | |
| startSmoothScroll(linearSmoothScroller) | |
| } | |
| } |
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