CollectionView中的自定义单元格重新排序行为

Question

我可以像这样重新排序我的collectionView:

但是,我不想将所有细胞水平移动,而是只想交换以下行为(即更少的细胞洗牌):

我一直在使用以下委托方法:

func collectionView(_ collectionView: UICollectionView, targetIndexPathForMoveFromItemAt originalIndexPath: IndexPath, toProposedIndexPath proposedIndexPath: IndexPath) -> IndexPath

但是,我不确定如何实现自定义重新排序行为.

Answer 1

我设法通过创建子类UICollectionView并为交互式移动添加自定义处理来实现此目的.在查看如何解决问题的可能提示时,我发现了本教程:http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/.最重要的部分是交互式重新排序不仅可以进行UICollectionViewController.相关代码如下所示:

var longPressGesture : UILongPressGestureRecognizer!

override func viewDidLoad() {
    super.viewDidLoad()

    // rest of setup        

    longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(ViewController.handleLongGesture(_:)))
    self.collectionView?.addGestureRecognizer(longPressGesture)

}

func handleLongGesture(gesture: UILongPressGestureRecognizer) {

    switch(gesture.state) {

    case UIGestureRecognizerState.Began:
        guard let selectedIndexPath = self.collectionView?.indexPathForItemAtPoint(gesture.locationInView(self.collectionView)) else {
            break
        }
        collectionView?.beginInteractiveMovementForItemAtIndexPath(selectedIndexPath)
    case UIGestureRecognizerState.Changed:
        collectionView?.updateInteractiveMovementTargetPosition(gesture.locationInView(gesture.view!))
    case UIGestureRecognizerState.Ended:
        collectionView?.endInteractiveMovement()
    default:
        collectionView?.cancelInteractiveMovement()
    }
}

这需要位于放置集合视图的视图控制器中.我不知道这是否UICollectionViewController合适,可能需要一些额外的修补.让我进行子类化的原因UICollectionView是认识到所有其他相关的类/委托方法只被告知第一个和最后一个索引路径(即源和目标),并且没有关于重新排列的所有其他单元的信息,所以它需要被阻止在核心.

SwappingCollectionView.swift:

import UIKit

extension UIView {
    func snapshot() -> UIImage {
        UIGraphicsBeginImageContext(self.bounds.size)
        self.layer.renderInContext(UIGraphicsGetCurrentContext()!)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}

extension CGPoint {
    func distanceToPoint(p:CGPoint) -> CGFloat {
        return sqrt(pow((p.x - x), 2) + pow((p.y - y), 2))
    }
}

struct SwapDescription : Hashable {
    var firstItem : Int
    var secondItem : Int

    var hashValue: Int {
        get {
            return (firstItem * 10) + secondItem
        }
    }
}

func ==(lhs: SwapDescription, rhs: SwapDescription) -> Bool {
    return lhs.firstItem == rhs.firstItem && lhs.secondItem == rhs.secondItem
}

class SwappingCollectionView: UICollectionView {

    var interactiveIndexPath : NSIndexPath?
    var interactiveView : UIView?
    var interactiveCell : UICollectionViewCell?
    var swapSet : Set<SwapDescription> = Set()
    var previousPoint : CGPoint?

    static let distanceDelta:CGFloat = 2 // adjust as needed

    override func beginInteractiveMovementForItemAtIndexPath(indexPath: NSIndexPath) -> Bool {

        self.interactiveIndexPath = indexPath

        self.interactiveCell = self.cellForItemAtIndexPath(indexPath)

        self.interactiveView = UIImageView(image: self.interactiveCell?.snapshot())
        self.interactiveView?.frame = self.interactiveCell!.frame

        self.addSubview(self.interactiveView!)
        self.bringSubviewToFront(self.interactiveView!)

        self.interactiveCell?.hidden = true

        return true
    }

    override func updateInteractiveMovementTargetPosition(targetPosition: CGPoint) {

        if (self.shouldSwap(targetPosition)) {

            if let hoverIndexPath = self.indexPathForItemAtPoint(targetPosition), let interactiveIndexPath = self.interactiveIndexPath {

                let swapDescription = SwapDescription(firstItem: interactiveIndexPath.item, secondItem: hoverIndexPath.item)

                if (!self.swapSet.contains(swapDescription)) {

                    self.swapSet.insert(swapDescription)

                    self.performBatchUpdates({
                        self.moveItemAtIndexPath(interactiveIndexPath, toIndexPath: hoverIndexPath)
                        self.moveItemAtIndexPath(hoverIndexPath, toIndexPath: interactiveIndexPath)
                        }, completion: {(finished) in
                            self.swapSet.remove(swapDescription)                                
                            self.dataSource?.collectionView(self, moveItemAtIndexPath: interactiveIndexPath, toIndexPath: hoverIndexPath)
                            self.interactiveIndexPath = hoverIndexPath

                    })
                }
            }
        }

        self.interactiveView?.center = targetPosition
        self.previousPoint = targetPosition
    }

    override func endInteractiveMovement() {
        self.cleanup()
    }

    override func cancelInteractiveMovement() {
        self.cleanup()
    }

    func cleanup() {
        self.interactiveCell?.hidden = false
        self.interactiveView?.removeFromSuperview()
        self.interactiveView = nil
        self.interactiveCell = nil
        self.interactiveIndexPath = nil
        self.previousPoint = nil
        self.swapSet.removeAll()
    }

    func shouldSwap(newPoint: CGPoint) -> Bool {
        if let previousPoint = self.previousPoint {
            let distance = previousPoint.distanceToPoint(newPoint)
            return distance < SwappingCollectionView.distanceDelta
        }

        return false
    }
}

我确实意识到那里有很多事情,但我希望一切都会在一分钟内清楚.

1. UIView使用辅助方法扩展以获取单元格的快照.
2. CGPoint使用辅助方法扩展以计算两点之间的距离.
3. SwapDescription辅助结构 - 需要防止同一对项目的多次交换,这导致了毛刺的动画.它的hashValue方法可以改进,但为了这个概念证明就足够了.
4. beginInteractiveMovementForItemAtIndexPath(indexPath: NSIndexPath) -> Bool - 移动开始时调用的方法.一切都在这里设置.我们获取单元格的快照并将其添加为子视图 - 此快照将是用户实际在屏幕上拖动的内容.细胞本身被隐藏起来.如果false从此方法返回,则不会开始交互式移动.
5. updateInteractiveMovementTargetPosition(targetPosition: CGPoint) - 每个用户移动后调用的方法,这很多.我们检查,如果从以前的点的距离小到足以交换项目 - 这样可以防止问题,当用户将快速拖动屏幕对面和多个项目将得到与非明显的效果交换.如果交换可能发生,我们检查它是否已经发生,如果不是,我们交换两个项目.
6. endInteractiveMovement(),cancelInteractiveMovement(),cleanup()-移动结束后,我们需要把我们的帮手恢复到默认状态.
7. shouldSwap(newPoint: CGPoint) -> Bool - 辅助方法检查运动是否足够小,以便我们可以交换细胞.

这是它给出的结果:

请告诉我这是否是您需要的和/或您是否需要我澄清一些事情.

这是一个演示项目.