128 lines
4.5 KiB
Swift
128 lines
4.5 KiB
Swift
//
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// GridCollectionViewLayout.swift
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// Delta
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//
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// Created by Riley Testut on 10/24/15.
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// Copyright © 2015 Riley Testut. All rights reserved.
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//
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import UIKit
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class GridCollectionViewLayout: UICollectionViewFlowLayout
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{
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var itemWidth: CGFloat = 150 {
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didSet {
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// Only invalidate if needed, otherwise could potentially cause endless loop
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if oldValue != self.itemWidth
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{
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self.invalidateLayout()
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}
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}
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}
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// If only one row, distribute the items equally horizontally
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var usesEqualHorizontalSpacingDistributionForSingleRow = false
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override var estimatedItemSize: CGSize {
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didSet {
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fatalError("GridCollectionViewLayout does not support self-sizing cells.")
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}
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}
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override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]?
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{
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guard let collectionView = self.collectionView else { return nil }
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let maximumItemsPerRow = floor((collectionView.bounds.width - self.minimumInteritemSpacing) / (self.itemWidth + self.minimumInteritemSpacing))
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let interitemSpacing = (collectionView.bounds.width - maximumItemsPerRow * self.itemWidth) / (maximumItemsPerRow + 1)
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self.sectionInset.left = interitemSpacing
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self.sectionInset.right = interitemSpacing
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let layoutAttributes = super.layoutAttributesForElements(in: rect)?.map({ $0.copy() }) as! [UICollectionViewLayoutAttributes]
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var minimumY: CGFloat? = nil
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var maximumY: CGFloat? = nil
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var tempLayoutAttributes: [UICollectionViewLayoutAttributes] = []
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var isSingleRow = true
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for (index, attributes) in layoutAttributes.enumerated()
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{
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guard attributes.representedElementCategory == .cell else { continue }
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// Ensure equal spacing between items (that also match the section insets)
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if index > 0
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{
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let previousLayoutAttributes = layoutAttributes[index - 1]
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if abs(attributes.frame.minX - self.sectionInset.left) > 1
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{
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attributes.frame.origin.x = previousLayoutAttributes.frame.maxX + interitemSpacing
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}
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}
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if let maxY = maximumY, let minY = minimumY
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{
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// If attributes.frame.minY is greater than maximumY, then it is a new row
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// In this case, we need to align all the previous tempLayoutAttributes to the same Y-value
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if attributes.frame.minY > maxY
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{
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isSingleRow = false
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self.alignLayoutAttributes(tempLayoutAttributes, toMinimumY: minY)
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// Reset tempLayoutAttributes
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tempLayoutAttributes.removeAll()
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minimumY = nil
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maximumY = nil
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}
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}
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// Update minimumY value if needed
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if minimumY == nil || attributes.frame.minY < minimumY!
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{
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minimumY = attributes.frame.minY
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}
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// Update maximumY value if needed
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if maximumY == nil || attributes.frame.maxY > maximumY!
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{
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maximumY = attributes.frame.maxY
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}
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tempLayoutAttributes.append(attributes)
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}
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// Handle the remaining tempLayoutAttributes
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if let minimumY = minimumY
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{
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self.alignLayoutAttributes(tempLayoutAttributes, toMinimumY: minimumY)
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if isSingleRow && self.usesEqualHorizontalSpacingDistributionForSingleRow
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{
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let spacing = (collectionView.bounds.width - (self.itemWidth * CGFloat(tempLayoutAttributes.count))) / (CGFloat(tempLayoutAttributes.count) + 1.0)
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for (index, layoutAttributes) in tempLayoutAttributes.enumerated()
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{
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layoutAttributes.frame.origin.x = spacing + (spacing + self.itemWidth) * CGFloat(index)
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}
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}
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}
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return layoutAttributes
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}
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}
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private extension GridCollectionViewLayout
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{
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func alignLayoutAttributes(_ layoutAttributes: [UICollectionViewLayoutAttributes], toMinimumY minimumY: CGFloat)
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{
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for attributes in layoutAttributes
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{
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attributes.frame.origin.y = minimumY
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}
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}
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}
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