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orioonyx/CenterZoomLayoutManager

Created January 8, 2023 14:23
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  1. orioonyx created this gist Jan 8, 2023.
    70 changes: 70 additions & 0 deletions CenterZoomLayoutManager
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,70 @@
    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)
    }
    }