ios - Swift 如何在 collectionView 中获取中心单元格并在滚动时调整它的大小？

Question

我有一个水平的 collectionView，我想在滚动它时管理它，中心单元格变大。因此，每次一个单元格成为中心单元格时，它都会比其他单元格大。检查下图。

谁能帮我找到最好的方法？提前致谢!

到目前为止我的代码:

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
}
}

Answer 1

试试这个:

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)
}

此代码为您提供 Collection View 中心的项目索引。希望这有帮助