Left aligned collection view flow layout.

UICollectionViewLeftAlignedLayout.swift

//  MIT License
//
//  Copyright (c) 2019 Balázs Vincze
//
//  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
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//  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

final class UICollectionViewLeftAlignedLayout: UICollectionViewFlowLayout {
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var newAttributesArray = [UICollectionViewLayoutAttributes]()
        let superAttributesArray = super.layoutAttributesForElements(in: rect)!
        for (index, attributes) in superAttributesArray.enumerated() {
            if index == 0 || superAttributesArray[index - 1].frame.origin.y != attributes.frame.origin.y {
                attributes.frame.origin.x = sectionInset.left
            } else {
                let previousAttributes = superAttributesArray[index - 1]
                let previousFrameRight = previousAttributes.frame.origin.x + previousAttributes.frame.width
                attributes.frame.origin.x = previousFrameRight + minimumInteritemSpacing
            }
            newAttributesArray.append(attributes)
        }
        return newAttributesArray
    }
}

Thank you for sharing code.
I add layoutAttributesForItem(at) method for collectionView.reloadItems(at) .

final class UICollectionViewLeftAlignedLayout: UICollectionViewFlowLayout {

  private var layouts: [IndexPath: UICollectionViewLayoutAttributes] = [:]

  override func prepare() {
    super.prepare()
    layouts = [:]
  }

  override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    var newAttributesArray = [UICollectionViewLayoutAttributes]()
    let superAttributesArray = super.layoutAttributesForElements(in: rect)!
    for (index, attributes) in superAttributesArray.enumerated() {
      if index == 0 || superAttributesArray[index - 1].frame.origin.y != attributes.frame.origin.y {
        attributes.frame.origin.x = sectionInset.left
      } else {
        let previousAttributes = superAttributesArray[index - 1]
        let previousFrameRight = previousAttributes.frame.origin.x + previousAttributes.frame.width
        attributes.frame.origin.x = previousFrameRight + minimumInteritemSpacing
      }
      newAttributesArray.append(attributes)
    }
    newAttributesArray.forEach { layouts[$0.indexPath] = $0 }
    return newAttributesArray
  }

  override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
    layouts[indexPath]
  }
}