Alex.k
124 lines
4.2 KiB
Swift
124 lines
4.2 KiB
Swift
//
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// CollectionViewStackFlowLayout.swift
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// NavigationStackDemo
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//
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// Created by Alex K. on 25/02/16.
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// Copyright © 2016 Alex K. All rights reserved.
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//
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import UIKit
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// MARK: CollectionViewStackFlowLayout
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class CollectionViewStackFlowLayout: UICollectionViewFlowLayout {
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let itemsCount: Int
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let overlay: Float // from 0 to 1
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let maxScale: Float
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let scaleRatio: Float
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var additionScale = 1.0
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var openAnimating = false
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var dxOffset: Float = 0
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init(itemsCount: Int, overlay: Float, scaleRatio: Float, scale: Float) {
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self.itemsCount = itemsCount
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self.overlay = overlay
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self.scaleRatio = scaleRatio
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self.maxScale = scale
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super.init()
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}
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required init?(coder aDecoder: NSCoder) {
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fatalError("init(coder:) has not been implemented")
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}
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}
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extension CollectionViewStackFlowLayout {
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override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
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let items = NSArray (array: super.layoutAttributesForElementsInRect(rect)!, copyItems: true)
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var headerAttributes: UICollectionViewLayoutAttributes?
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items.enumerateObjectsUsingBlock { (object, idex, stop) -> Void in
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let attributes = object as! UICollectionViewLayoutAttributes
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if attributes.representedElementKind == UICollectionElementKindSectionHeader {
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headerAttributes = attributes
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}
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else {
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self.updateCellAttributes(attributes, headerAttributes: headerAttributes)
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}
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}
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return items as? [UICollectionViewLayoutAttributes]
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}
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func updateCellAttributes(attributes: UICollectionViewLayoutAttributes, headerAttributes: UICollectionViewLayoutAttributes?) {
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guard let collectionView = self.collectionView else {
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return;
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}
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let itemWidth = collectionView.bounds.size.width - collectionView.bounds.size.width * CGFloat(overlay)
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let allWidth = itemWidth * CGFloat(itemsCount - 1)
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// set contentOffset range
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let contentOffsetX = min(max(0, collectionView.contentOffset.x), allWidth)
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let scale = transformScale(attributes, allWidth: allWidth, offset: contentOffsetX)
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let move = transformMove(attributes, itemWidth: itemWidth, offset: contentOffsetX)
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attributes.transform = CGAffineTransformConcat(scale, move)
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attributes.alpha = calculateAlpha(attributes, itemWidth: itemWidth, offset: contentOffsetX)
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if additionScale > 0 && openAnimating {
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additionScale -= 0.02
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}
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attributes.zIndex = attributes.indexPath.row
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}
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override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
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return true
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}
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}
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// MARK: helpers
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extension CollectionViewStackFlowLayout {
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private func transformScale(attributes: UICollectionViewLayoutAttributes, allWidth: CGFloat, offset: CGFloat) -> CGAffineTransform {
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var maximum = CGFloat(maxScale) - CGFloat(itemsCount - attributes.indexPath.row) / CGFloat(scaleRatio)
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maximum += CGFloat(1.0 - maximum) * CGFloat(additionScale)
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var minimum = CGFloat(maxScale - 0.1) - CGFloat(itemsCount - attributes.indexPath.row) / CGFloat(scaleRatio)
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minimum += CGFloat(1.0 - minimum) * CGFloat(additionScale)
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var currentScale = (maximum + minimum) - (minimum + offset / (allWidth / (maximum - minimum)))
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currentScale = max(min(maximum, currentScale), minimum)
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return CGAffineTransformMakeScale(currentScale, currentScale)
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}
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private func transformMove(attributes: UICollectionViewLayoutAttributes, itemWidth: CGFloat, offset: CGFloat) -> CGAffineTransform {
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var currentContentOffsetX = offset - itemWidth * CGFloat(attributes.indexPath.row)
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currentContentOffsetX = min(max(currentContentOffsetX, 0),itemWidth)
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var dx = (currentContentOffsetX / itemWidth)
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if let collectionView = self.collectionView {
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dx *= collectionView.bounds.size.width / 8.0
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}
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dx = currentContentOffsetX - dx
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return CGAffineTransformMakeTranslation(dx, 0)
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}
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private func calculateAlpha(attributes: UICollectionViewLayoutAttributes, itemWidth: CGFloat, offset: CGFloat) -> CGFloat {
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var currentContentOffsetX = offset - itemWidth * CGFloat(attributes.indexPath.row)
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currentContentOffsetX = min(max(currentContentOffsetX, 0),itemWidth)
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let dx = (currentContentOffsetX / itemWidth)
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return 1.0 - dx
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}
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}
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