1、头部拉伸效果

headerGrag.gif

1.继承UICollectionViewFlowLayout
2.方法override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool需要返回true,否则重写无效
3.拿出所有布局内容数组,找到elementKindSectionHeader
4.判断是否是下拉,既contentOffset.y是否小于0
5.重写frame

import UIKit

class HeaderDragLayout: UICollectionViewFlowLayout {

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let layoutAttributes = super.layoutAttributesForElements(in: rect)
        for layout in layoutAttributes! {
            /** 1.判断是否是头部视图 */
            if layout.representedElementKind == UICollectionView.elementKindSectionHeader {
                let contentOffSetY: CGFloat = self.collectionView?.contentOffset.y ?? 0
                /** 2.判断是否下拉 */
                if contentOffSetY < CGFloat(0) {
                    /** 3.重新设置头部视图的起始位置和高度 */
                    layout.frame = CGRect(x: layout.frame.minX, y: contentOffSetY, width: layout.frame.width, height: layout.frame.height - contentOffSetY)
                }
            }     
        }
        return layoutAttributes
    }
    
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}

2、距离中心点越远,缩放越大

滚动图片.gif

1.继承UICollectionViewFlowLayout
2.方法override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool需要返回true,否则重写无效
3.找出滚动到的item的中心点位置centerX
4.使用abs()获取绝对距离
5.计算缩放的范围(这里只是简单的做了一些算术题,主要是实现思路....)
6.最后设置每一个item的transform
7.重新设置中心点位置,这里用到了四舍五入方法round()

import UIKit

class ScrollLayout: UICollectionViewFlowLayout {

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let customLayouts = super.layoutAttributesForElements(in: rect)
        
        if self.scrollDirection == .horizontal {
            let centerX = CGFloat((self.collectionView?.contentOffset.x)!) + CGFloat((self.collectionView?.bounds.size.width)!*0.5)
            for layout in customLayouts! {
                /// item中心点与界面中心的距离
                let center = abs(layout.center.x - centerX)
                let scale = 1/(1+center/((self.collectionView?.bounds.size.width)! - self.minimumLineSpacing))
                
                layout.transform = CGAffineTransform(scaleX: scale, y: scale)
            }
        } else {
            let centerY = CGFloat((self.collectionView?.contentOffset.y)!) + CGFloat((self.collectionView?.bounds.size.height)!*0.5)
            for layout in customLayouts! {
                /// item中心点与界面中心的距离
                let center = abs(layout.center.y - centerY)
                let scale = 1/(1+center/((self.collectionView?.bounds.size.height)! - self.minimumLineSpacing))
                
                layout.transform = CGAffineTransform(scaleX: scale, y: scale)
            }
        }

        return customLayouts
    }
    
    /// 重新设置中心点位置
    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
        var point = super.targetContentOffset(forProposedContentOffset: proposedContentOffset, withScrollingVelocity: velocity)
        if self.scrollDirection == .horizontal {
            let page = round(proposedContentOffset.x/(self.itemSize.width + self.minimumLineSpacing))
            let pageX = self.itemSize.width * (page + 0.5) - (self.collectionView?.bounds.size.width)! * 0.5 + self.minimumLineSpacing*page
            point.x = pageX
        }
        else {
            let page = round(proposedContentOffset.y/(self.itemSize.height + self.minimumLineSpacing))
            let pageY = self.itemSize.height * (page + 0.5) - (self.collectionView?.bounds.size.height)! * 0.5 + self.minimumLineSpacing*page
            point.y = pageY
        }
        
        return point
    }
    
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}

3、item的选中和移动

itemDrag.gif

本例中没有重新操作数据源

1.声明UICollectionViewDragDelegate, UICollectionViewDropDelegate
2.声明代理时记得collectionView.dragInteractionEnabled = true
3.代理方法
optional func collectionView(_ collectionView: UICollectionView, dragPreviewParametersForItemAt indexPath: IndexPath) -> UIDragPreviewParameters?
实现选中item后的一些基础设置,包括如:、贝塞尔曲线. 、item的背景色
4.代理方法 func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator)实现拖动停止后的后续操作

extension LevelViewController: UICollectionViewDragDelegate, UICollectionViewDropDelegate {
    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        let itemProvider = NSItemProvider.init()
        let drag = UIDragItem.init(itemProvider: itemProvider)
        return [drag]
    }
    
    /** 被选中以后可执行的操作:1、设置贝塞尔曲线 2、设置背景颜色 */
    func collectionView(_ collectionView: UICollectionView, dragPreviewParametersForItemAt indexPath: IndexPath) -> UIDragPreviewParameters? {
        let path = UIBezierPath.init(roundedRect: CGRect(origin: CGPoint(x: 0, y: 0), size: cellSize), cornerRadius: 18)
        let parameters = UIDragPreviewParameters.init()
        parameters.backgroundColor = UIColor.gray
        parameters.visiblePath = path
        
        return parameters
    }
    
    func collectionView(_ collectionView: UICollectionView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem] {
        let itemProvider = NSItemProvider.init()
        let drag = UIDragItem.init(itemProvider: itemProvider)
        
        return [drag]
    }
    
    func collectionView(_ collectionView: UICollectionView, dragSessionDidEnd session: UIDragSession) {

    }
    
    func collectionView(_ collectionView: UICollectionView, dragSessionWillBegin session: UIDragSession) {
        
    }
    
    func collectionView(_ collectionView: UICollectionView, dragSessionAllowsMoveOperation session: UIDragSession) -> Bool {
        return true
    }
    
    func collectionView(_ collectionView: UICollectionView, dragSessionIsRestrictedToDraggingApplication session: UIDragSession) -> Bool {
        return true
    }
    
 
    // MARK:---------------  UICollectionViewDropDelegate ---------------
    func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {
    
        let dropProposal = UICollectionViewDropProposal.init(operation: .move, intent: .insertAtDestinationIndexPath)
        return dropProposal
    }
    
    func collectionView(_ collectionView: UICollectionView, performAction action: Selector, forItemAt indexPath: IndexPath, withSender sender: Any?) {
        
    }
    
    func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator) {
        guard let endIndexPath: IndexPath = coordinator.destinationIndexPath else {return}
        guard let beginIndexPath: IndexPath = coordinator.items.first?.sourceIndexPath else {return}
        collectionView.moveItem(at: beginIndexPath, to: endIndexPath)
    }
    
    func collectionView(_ collectionView: UICollectionView, canHandle session: UIDropSession) -> Bool {
        return true
    }
    
    func collectionView(_ collectionView: UICollectionView, dropSessionDidEnter session: UIDropSession) {

    }
}

[代码在这里:]https://gitee.com/wuchuantao_admin/CTCollectionViewDemo