TagsView with CollectionView

UICollectionViewFlowLayout (left alignment)

type 1

class FlowLayout: UICollectionViewFlowLayout {
  override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
    var attributesForElementsInRect = super.layoutAttributesForElementsInRect(rect)
    var newAttributesForElementsInRect = [AnyObject]()
    // use a value to keep track of left margin
    var leftMargin: CGFloat = 0.0;
    for attributes in attributesForElementsInRect! {
      var refAttributes = attributes as! UICollectionViewLayoutAttributes
      // assign value if next row
      if (refAttributes.frame.origin.x == self.sectionInset.left) {
        leftMargin = self.sectionInset.left
      } else {
        // set x position of attributes to current margin
        var newLeftAlignedFrame = refAttributes.frame
        newLeftAlignedFrame.origin.x = leftMargin 
        refAttributes.frame = newLeftAlignedFrame
      }
      // calculate new value for current margin
      leftMargin += refAttributes.frame.size.width
      newAttributesForElementsInRect.append(refAttributes)
    }
    return newAttributesForElementsInRect
  }
}

type 2

class CollectionViewFlowLayoutLeftAlign: UICollectionViewFlowLayout {
    override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        guard let attributes = super.layoutAttributesForElementsInRect(rect) else {             
            return nil
        }

        var attributesToReturn = attributes.map { $0.copy() as! UICollectionViewLayoutAttributes }
        for (index, attr) in attributes.enumerate() where attr.representedElementCategory == .Cell {
            attributesToReturn[index] = layoutAttributesForItemAtIndexPath(attr.indexPath) ?? UICollectionViewLayoutAttributes()
        }
        return attributesToReturn
    }

    override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
        guard let currentAttributes = super.layoutAttributesForItemAtIndexPath(indexPath)?.copy() as? UICollectionViewLayoutAttributes,
              let viewWidth = collectionView?.frame.width else {
                return nil
        }

        let sectionInsetsLeft = sectionInsets(at: indexPath.section).left

        guard indexPath.item > 0 else {
            currentAttributes.frame.origin.x = sectionInsetsLeft
            return currentAttributes
        }

        let prevIndexPath = NSIndexPath(forItem: indexPath.item - 1, inSection: indexPath.section)
        guard let prevFrame = layoutAttributesForItemAtIndexPath(prevIndexPath)?.frame else {
            return nil
        }
        let validWidth = viewWidth - sectionInset.left - sectionInset.right
        let currentColumnRect = CGRectMake(sectionInsetsLeft, currentAttributes.frame.origin.y, validWidth, currentAttributes.frame.height)
        guard CGRectIntersectsRect(prevFrame, currentColumnRect) else {
            currentAttributes.frame.origin.x = sectionInsetsLeft
            return currentAttributes
        }

        let prevItemTailX = prevFrame.origin.x + prevFrame.width
        currentAttributes.frame.origin.x = prevItemTailX + minimumInteritemSpacing(at: indexPath.section)
        return currentAttributes
    }

    private func sectionInsets(at index: Int) -> UIEdgeInsets {
        guard
            let collectionView = collectionView,
            let delegate = collectionView.delegate as? UICollectionViewDelegateFlowLayout else {
                return self.sectionInset
        }
        return delegate.collectionView?(collectionView, layout: self, insetForSectionAtIndex: index) ?? self.sectionInset
    }

    private func minimumInteritemSpacing(at index: Int) -> CGFloat {
        guard
            let collectionView = collectionView,
            let delegate = collectionView.delegate as? UICollectionViewDelegateFlowLayout else {
                return self.minimumInteritemSpacing
        }
        return delegate.collectionView?(collectionView, layout: self, minimumInteritemSpacingForSectionAtIndex: index) ?? self.minimumInteritemSpacing
    }
}