UICollectionView 检测滚动方向和更改图像

Question

我正在使用 UICollectionView 创建类似于 Tinder Swipe 的滑动。 当用户在显示新页面（卡片）之前开始拖动时，我想检测滚动方向。当它被检测到时，它应该将图像设置为拇指向上（向右滑动）或拇指向下（向左滑动）。

现在我使用 scrollViewWillBeginDragging 并且它几乎可以用于比较 contentOffset 但这不是我想要的，因为它显示图像很晚。

import UIKit

class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, UIGestureRecognizerDelegate{

    var imageArray = [UIImage(named: "profil"), UIImage(named: "profil"),UIImage(named: "profil"),UIImage(named: "profil"),UIImage(named: "profil"),UIImage(named: "profil"),UIImage(named: "profil")]

    @IBOutlet weak var thumbImage: UIImageView!
    var currentPage = 0

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCollectionViewCell", for: indexPath) as! ImageCollectionViewCell

        cell.imgImage.image = imageArray[indexPath.row]
        cell.backgroundColor = indexPath.item % 2 == 0 ? .red : .green

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

        return CGSize(width: collectionView.frame.width, height: collectionView.frame.height)
    } 


    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {

        var page = Int(scrollView.contentOffset.x / scrollView.frame.size.width)

        if(page > currentPage)
        {
            thumbImage.isHidden = false
            thumbImage.image = #imageLiteral(resourceName: "thumbsup")
            print("RIGHT")
        } else {
            thumbImage.isHidden = false
            thumbImage.image = #imageLiteral(resourceName: "thumbsdown")
            print("LEFT")
        }

        currentPage = page

    }
}

Answer 1

在您当前的实现中，拇指图像仅在页面发生变化时显示，即滑动到一半时。我会将页面更改与拇指显示分开。伪代码：

if (currentOffset > lastOffset) {
    showThumbsUp()
}
else {
    showThumbsDown()
}

page = ...
if (page != currentPage) {
    changePage(page)
    lastOffset = currentOffset
}