NSCollectionViewFlowLayout - 左对齐

NSCollectionViewFlowLayout 生成一个布局，其中的项目在右边缘对齐，或者，如果容器的宽度仅足以容纳一个项目，则将项目居中。我期待一个对齐选项，例如在代表上，但我在文档中没有找到任何内容。是否需要子类化 NSCollectionViewFlowLayout 才能实现此目的？

这是一个生成左对齐流布局的子类：

class LeftFlowLayout: NSCollectionViewFlowLayout {

    override func layoutAttributesForElementsInRect(rect: CGRect) -> [NSCollectionViewLayoutAttributes] {

        let defaultAttributes = super.layoutAttributesForElementsInRect(rect)

        if defaultAttributes.isEmpty {
            // we rely on 0th element being present,
            // bail if missing (when there's no work to do anyway)
            return defaultAttributes
        }

        var leftAlignedAttributes = [NSCollectionViewLayoutAttributes]()

        var xCursor = self.sectionInset.left // left margin

        // if/when there is a new row, we want to start at left margin
        // the default FlowLayout will sometimes centre items,
        // i.e. new rows do not always start at the left edge

        var lastYPosition = defaultAttributes[0].frame.origin.y

        for attributes in defaultAttributes {
            if attributes.frame.origin.y > lastYPosition {
                // we have changed line
                xCursor = self.sectionInset.left
                lastYPosition = attributes.frame.origin.y
            }

            attributes.frame.origin.x = xCursor
            // by using the minimumInterimitemSpacing we no we'll never go
            // beyond the right margin, so no further checks are required
            xCursor += attributes.frame.size.width + minimumInteritemSpacing

            leftAlignedAttributes.append(attributes)
        }
        return leftAlignedAttributes
    }
}