Centered!

Author: Coeur

.gitignore

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+**/xcuserdata/**

CollectionViewCenteredFlowLayout.podspec

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+version = "1.0.0"
+
+Pod::Spec.new do |s|
+  s.name         = 'CollectionViewCenteredFlowLayout'
+  s.version      = version
+  s.summary      = 'A layout for UICollectionView that aligns the cells to the center'
+  s.description  = <<-DESC
+                   A `UICollectionViewLayout` implementation that aligns the cells to the center.
+
+                   It uses `UICollectionViewFlowLayout` under the hood.
+                   DESC
+  s.homepage     = 'https://github.com/coeur/CollectionViewCenteredFlowLayout'
+  s.screenshots  = 'https://raw.githubusercontent.com/coeur/CollectionViewCenteredFlowLayout/master/screenshot.png'
+  s.license      = { :type => "MIT", :file => "LICENSE" }
+  s.authors      = { 'Antoine Cœur' => '' }
+  s.social_media_url   = 'http://twitter.com/adigitalknight'
+  s.platform     = :ios, '8.0'
+  s.source       = { :git => 'https://github.com/coeur/CollectionViewCenteredFlowLayout.git', :tag => version }
+  s.source_files  = 'CollectionViewCenteredFlowLayout/*.swift'
+end

CollectionViewCenteredFlowLayout/CollectionViewCenteredFlowLayout.swift

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+
+// Copyright (c) 2017 Cœur
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of
+// this software and associated documentation files (the "Software"), to deal in
+// the Software without restriction, including without limitation the rights to
+// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+// the Software, and to permit persons to whom the Software is furnished to do so,
+// subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+// CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+import UIKit
+
+/**
+ *  Simple UICollectionViewFlowLayout that centers the cells rather than justify them
+ *
+ *  Based on https://github.com/Coeur/UICollectionViewLeftAlignedLayout
+ */
+open class CollectionViewCenteredFlowLayout: UICollectionViewFlowLayout {
+    open override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
+        guard let layoutAttributesForElements = super.layoutAttributesForElements(in: rect) else {
+            return nil
+        }
+        guard let collectionView = collectionView else {
+            return layoutAttributesForElements
+        }
+        // we group copies of the elements from the same row/column
+        var representedElements: [UICollectionViewLayoutAttributes] = []
+        var cells: [[UICollectionViewLayoutAttributes]] = [[]]
+        var previousFrame: CGRect? = nil
+        for layoutAttributes in layoutAttributesForElements {
+            guard layoutAttributes.representedElementKind == nil else {
+                representedElements.append(layoutAttributes)
+                continue
+            }
+            let currentItemAttributes = layoutAttributes.copy() as! UICollectionViewLayoutAttributes
+            if previousFrame != nil {
+                if scrollDirection == .vertical {
+                    // if the current frame, once stretched to the full row intersects the previous frame then they are on the same row
+                    if !currentItemAttributes.frame.intersects(CGRect(x: -.infinity, y: previousFrame!.origin.y, width: .infinity, height: previousFrame!.size.height)) {
+                        // the item is on a different row
+                        cells.append([])
+                    }
+                } else {
+                    // if the current frame, once stretched to the full column intersects the previous frame then they are on the same column
+                    if !currentItemAttributes.frame.intersects(CGRect(x: previousFrame!.origin.x, y: -.infinity, width: previousFrame!.size.width, height: .infinity)) {
+                        // the item is on a different column
+                        cells.append([])
+                    }
+                }
+            }
+            cells[cells.endIndex - 1].append(currentItemAttributes)
+            previousFrame = currentItemAttributes.frame
+        }
+        return representedElements + cells.flatMap { group -> [UICollectionViewLayoutAttributes] in
+            guard !group.isEmpty else {
+                return group
+            }
+            let section = group.first!.indexPath.section
+            let evaluatedSectionInset = (collectionView.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView?(collectionView, layout: self, insetForSectionAt: section) ?? sectionInset
+            let evaluatedMinimumInteritemSpacing = (collectionView.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView?(collectionView, layout: self, minimumInteritemSpacingForSectionAt: section) ?? minimumInteritemSpacing
+            if scrollDirection == .vertical {
+                var origin = (collectionView.bounds.width + evaluatedSectionInset.left - evaluatedSectionInset.right - group.reduce(0, { $0 + $1.frame.size.width }) - CGFloat(group.count - 1) * evaluatedMinimumInteritemSpacing) / 2
+                return group.map {
+                    $0.frame.origin.x = origin
+                    origin += $0.frame.size.width + evaluatedMinimumInteritemSpacing
+                    return $0
+                }
+            } else {
+                var origin = (collectionView.bounds.height + evaluatedSectionInset.top - evaluatedSectionInset.bottom - group.reduce(0, { $0 + $1.frame.size.height }) - CGFloat(group.count - 1) * evaluatedMinimumInteritemSpacing) / 2
+                return group.map {
+                    $0.frame.origin.y = origin
+                    origin += $0.frame.size.height + evaluatedMinimumInteritemSpacing
+                    return $0
+                }
+            }
+        }
+    }
+}