Swift How to get the centre cell in a collectionView and resize it when scrolling?

问题

I have a horizontal collectionView and i would like to manage that when scrolling it, the centre cell becomes larger. So, each time a cell is the center cell it will be larger than the others. Check the image beneath.

Can anyone help me with the best way to do this? Thanks in advance!

My code so far:

import UIKit

class ViewController: UIViewController, UICollectionViewDataSource,      UICollectionViewDelegate {
@IBOutlet var horizontalCollectionView: UICollectionView!
@IBOutlet var verticalCollectionView: UICollectionView!

var horizontal = ["1","2","3","4","5","6","7","8","9","10","1","2","3","4","5","6","7","8","9","10"]
var horizontalCellSize = CGSize(width: 50, height: 50)
var horizontalLargeCellSize = CGSize(width: 80, height: 80)


var centerCell = UICollectionViewCell()
var cellIsInCenter = false
var myIndexPath = IndexPath()

override func viewDidLoad() {
    super.viewDidLoad()

}

// When the main view's dimensions change this will re-layout the collection view
override func viewWillLayoutSubviews() {
    verticalCollectionView.collectionViewLayout.invalidateLayout()
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return horizontal.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    if collectionView == horizontalCollectionView {
        let horizontalCell = collectionView.dequeueReusableCell(withReuseIdentifier: "HorizontalCell", for: indexPath) as! HorizontalCell
        horizontalCell.backgroundColor = UIColor.blue
        horizontalCell.textLabel.text = horizontal[indexPath.row]
        return horizontalCell
    }

   else {

        let verticalCell = collectionView.dequeueReusableCell(withReuseIdentifier: "VerticalCell", for: indexPath) as! VerticalCell
        verticalCell.backgroundColor = UIColor.red
        verticalCell.textLabel.text = horizontal[indexPath.row]
        return verticalCell
    }
}

// MARK: UIScrollViewDelegate

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if scrollView == self.horizontalCollectionView {
        let horizontalScrollPosition = scrollView.contentOffset.x * 35
        self.verticalCollectionView.delegate = nil
        self.verticalCollectionView.contentOffset = CGPoint(x: 0, y: horizontalScrollPosition)
        self.verticalCollectionView.delegate = self
    }

    if scrollView == self.verticalCollectionView {
        let verticalScrollPosition = scrollView.contentOffset.y
        self.horizontalCollectionView.delegate = nil
        self.horizontalCollectionView.contentOffset = CGPoint(x: verticalScrollPosition, y: 0)
        self.horizontalCollectionView.delegate = self 
    }
}


// MARK: CollectionViewLayout

func collectionView(_ collectionView: UICollectionView,
                    layout collectionViewLayout: UICollectionViewLayout,
                    sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    if collectionView == verticalCollectionView {
        let size = CGSize(width: collectionView.bounds.width, height: collectionView.bounds.height)

        return size
    }

    if indexPath.item == 3 {
        return CGSize(width: 70, height: 70)
    }
    return CGSize(width: 50, height: 50)

}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    self.verticalCollectionView.scrollToItem(at: indexPath, at: .centeredVertically, animated: true)
    print("\(indexPath)")
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    var closestCell: UICollectionViewCell = self.horizontalCollectionView.visibleCells[0]
    for cell in self.horizontalCollectionView.visibleCells as [UICollectionViewCell] {
        let closestCellDelta = abs(closestCell.center.x - self.horizontalCollectionView.bounds.size.width / 2.0 - self.horizontalCollectionView.contentOffset.x)
        let cellDelta = abs(cell.center.x - self.horizontalCollectionView.bounds.size.width/2.0 - self.horizontalCollectionView.contentOffset.x)
        if (cellDelta < closestCellDelta){
            closestCell = cell
            self.centerCell = cell
            self.cellIsInCenter = true
            horizontalCellSize = CGSize(width: 80, height: 50)
        }
    }
    let indexPath = self.horizontalCollectionView.indexPath(for: closestCell)
    self.horizontalCollectionView.scrollToItem(at: indexPath!, at: .centeredHorizontally , animated: true)
    if closestCell.backgroundColor == UIColor.black {
        closestCell.backgroundColor = UIColor.blue
    }
    horizontalCollectionView.reloadItems(at: [self.horizontalCollectionView.indexPath(for: closestCell)!])
    closestCell.backgroundColor = UIColor.black
}
}

回答1:

Try this out:

func collectionView(_ collectionView: UICollectionView,layout collectionViewLayout: UICollectionViewLayout,
sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
if collectionView == verticalCollectionView {
let size = CGSize(width: collectionView.bounds.width, height: collectionView.bounds.height)
        return size
    }
let point = CGPoint(x: self.view.frame.size.width/2.0, y:35 )
//or you can try this code also
//let point = CGPoint(x: UIScreen.main.bounds.width/2, y:35 )
    print(point)
let centerIndex = self.collectionView.indexPathForItemAtPoint(point)
    if indexPath.item == centerIndex {
        return CGSize(width: 70, height: 70)
    }
    return CGSize(width: 50, height: 50)
}

This code gives you the index of the item at the center of the collection View. Hope this helps

来源：https://stackoverflow.com/questions/40741161/swift-how-to-get-the-centre-cell-in-a-collectionview-and-resize-it-when-scrollin