Fixed distance between an element in a UICollectionView with a layout

Question

So, I'm trying to implement a tag list using a UICollectionView. I follow this guide: http://www.cocoanetics.com/2013/08/variable-sized-items-in-uicollectionview/

The problem is the layout of the stream in the UICollectionView, which is trying to evenly position elements on the same line.

As a developer, I can specify a minimumInteritemSpacingForSectionAtIndex , this is really up to the UICollectionView to determine the actual distance between points.

But I really want to achieve this:

Any ideas?

Answer 1

Swift: https://github.com/Coeur/UICollectionViewLeftAlignedLayout/

UICollectionViewFlowLayout.

import UIKit

/**
 *  Simple UICollectionViewFlowLayout that aligns the cells to the left rather than justify them
 *
 *  Based on https://stackoverflow.com/questions/13017257/how-do-you-determine-spacing-between-cells-in-uicollectionview-flowlayout
 */
open class UICollectionViewLeftAlignedLayout: UICollectionViewFlowLayout {
    open override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return super.layoutAttributesForElements(in: rect)?.map { $0.representedElementKind == nil ? layoutAttributesForItem(at: $0.indexPath)! : $0 }
    }

    open override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        guard let currentItemAttributes = super.layoutAttributesForItem(at: indexPath)?.copy() as? UICollectionViewLayoutAttributes,
            let collectionView = self.collectionView else {
            // should never happen
            return nil
        }

        let sectionInset = evaluatedSectionInsetForSection(at: indexPath.section)

        guard indexPath.item != 0 else {
            currentItemAttributes.leftAlignFrame(withSectionInset: sectionInset)
            return currentItemAttributes
        }

        guard let previousFrame = layoutAttributesForItem(at: IndexPath(item: indexPath.item - 1, section: indexPath.section))?.frame else {
            // should never happen
            return nil
        }

        // if the current frame, once left aligned to the left and stretched to the full collection view
        // widht intersects the previous frame then they are on the same line
        guard previousFrame.intersects(CGRect(x: sectionInset.left, y: currentItemAttributes.frame.origin.y, width: collectionView.frame.width - sectionInset.left - sectionInset.right, height: currentItemAttributes.frame.size.height)) else {
            // make sure the first item on a line is left aligned
            currentItemAttributes.leftAlignFrame(withSectionInset: sectionInset)
            return currentItemAttributes
        }

        currentItemAttributes.frame.origin.x = previousFrame.origin.x + previousFrame.size.width + evaluatedMinimumInteritemSpacingForSection(at: indexPath.section)
        return currentItemAttributes
    }

    func evaluatedMinimumInteritemSpacingForSection(at section: NSInteger) -> CGFloat {
        return (collectionView?.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView?(collectionView!, layout: self, minimumInteritemSpacingForSectionAt: section) ?? minimumInteritemSpacing
    }

    func evaluatedSectionInsetForSection(at index: NSInteger) -> UIEdgeInsets {
        return (collectionView?.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView?(collectionView!, layout: self, insetForSectionAt: index) ?? sectionInset
    }
}

extension UICollectionViewLayoutAttributes {
    func leftAlignFrame(withSectionInset sectionInset: UIEdgeInsets) {
        frame.origin.x = sectionInset.left
    }
}

Answer 2

Apple UICollectionViewFlowLayout , " " . , , , . - , UICollectionViewLayout.

Apple WWDC 2012 " "

Apple: https://developer.apple.com/library/ios/documentation/WindowsViews/Conceptual/CollectionViewPGforIOS/CreatingCustomLayouts/CreatingCustomLayouts.html

- , , : http://bradbambara.wordpress.com/2014/05/24/getting-started-with-custom-uicollectionview-layouts/

, .