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Scrolling item on a horizontal UICollectionView, stopped item on center of screen.
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//: Playground - noun: a place where people can play | |
import UIKit | |
import PlaygroundSupport | |
class WLCollectionCell: UICollectionViewCell { | |
required init?(coder aDecoder: NSCoder) { | |
fatalError("init(coder:) has not been implemented") | |
} | |
override init(frame: CGRect) { | |
super.init(frame: frame) | |
setup() | |
} | |
func setup() { | |
self.layer.borderWidth = 1.0 | |
self.layer.borderColor = UIColor.red.cgColor | |
self.layer.cornerRadius = 5.0 | |
self.backgroundColor = UIColor.white | |
} | |
} | |
class WLCollectionViewLayout: UICollectionViewFlowLayout { | |
var previousOffset: CGFloat = 0 | |
var currentPage: Int = 0 | |
override func prepare() { | |
} | |
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint { | |
guard let collectionView = self.collectionView else { | |
return CGPoint.zero | |
} | |
guard let itemsCount = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: 0) else { | |
return CGPoint.zero | |
} | |
if ((previousOffset > collectionView.contentOffset.x) && (velocity.x < 0)) { | |
currentPage = max(currentPage - 1, 0) | |
} else if ((previousOffset < collectionView.contentOffset.x) && (velocity.x > 0.0)) { | |
currentPage = min(currentPage + 1, itemsCount - 1); | |
} | |
let itemEdgeOffset:CGFloat = (collectionView.frame.width - itemSize.width - minimumLineSpacing * 2) / 2 | |
let updatedOffset: CGFloat = (itemSize.width + minimumLineSpacing) * CGFloat(currentPage) - (itemEdgeOffset + minimumLineSpacing); | |
previousOffset = updatedOffset; | |
return CGPoint(x: updatedOffset, y: proposedContentOffset.y); | |
} | |
} | |
class RootVC: UIViewController, UICollectionViewDataSource { | |
var collectionView: UICollectionView? | |
var collectionLayout: WLCollectionViewLayout = WLCollectionViewLayout() | |
override func viewDidLoad() { | |
super.viewDidLoad() | |
/* | |
* | |
|<------- view width -------->| | |
--------------------------------------- | |
| | | |
|<-w0->|<ws>|<-- wi -->|<ws>|<-w0->| | |
--------------- --------------- --------------- | |
| | | | | | | |
| | | | | | | |
--------------- --------------- --------------- | |
| | | |
| | | |
--------------------------------------- | |
* | |
* w0: itemEdgeOffset | |
* ws: space | |
* wi: itemWidth | |
* in this example: ws == w0 | |
*/ | |
let space: CGFloat = 30 | |
self.view = UIView(frame: CGRect(x: 0, y: 0, width: 400, height: 600)) | |
self.view.backgroundColor = UIColor.blue | |
let collectionFrame = CGRect(x: 0, y: 60, width: view.frame.width, height: 200) | |
self.collectionView = UICollectionView(frame: collectionFrame, collectionViewLayout: collectionLayout) | |
collectionView?.register(WLCollectionCell.self, forCellWithReuseIdentifier: "CELL") | |
collectionView?.backgroundColor = self.view.backgroundColor | |
collectionView?.dataSource = self | |
collectionView?.isPagingEnabled = false | |
collectionView?.contentInset = UIEdgeInsets(top: 0, left: space, bottom: 0, right: space) | |
collectionLayout.scrollDirection = .horizontal | |
let itemWidth = view.frame.width - space * 4 // w0 == ws | |
collectionLayout.itemSize = CGSize(width: itemWidth, height: 180) | |
collectionLayout.minimumLineSpacing = space | |
self.view.addSubview(self.collectionView!) | |
} | |
func numberOfSections(in collectionView: UICollectionView) -> Int { | |
return 1 | |
} | |
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int { | |
return 4 | |
} | |
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { | |
if let cell: WLCollectionCell = collectionView.dequeueReusableCell(withReuseIdentifier: "CELL", for: indexPath) as? WLCollectionCell { | |
return cell | |
} | |
return UICollectionViewCell() | |
} | |
} | |
let vc = RootVC() | |
PlaygroundPage.current.liveView = vc.view | |
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good and simple thanks