Swift 3-iOS 11.2上的UICollectionview问题

我有两个问题 UICollectionView . 以下是场景:

问题1

我有一个在Xcode 8中创建的应用程序。它基于iOS 10.3模拟器,一切都很好。但当我在iOS 11.2设备上试用时,我发现 UICollectionView . 当一个新的数据出现时,它应该出现在底部(这是我想要的,也是我在iOS 10.3上所做的)。但iOS 11.2允许在新数据位于底部时滚动到顶部。

问题2

然后我从Xcode 8迁移到了Xcode 9.2,因为Xcode 8不直接支持iOS 11。但现在在Xcode 9.2 iOS 11.2模拟器上,我无法清晰地滚动collectionview,然后它就出现了 UIAppDelegate 具有 Thread 1: signal SIGABRT.

只要我知道,每当我断开插座时,就会出现这种错误。但我很确定我所有的渠道都有联系。

import UIKit

class cvViewController: UIViewController, UICollectionViewDataSource, UIImagePickerControllerDelegate, UINavigationControllerDelegate, UICollectionViewDelegate {

@IBOutlet var collectionView: UICollectionView!

override func viewDidLoad() {
    super.viewDidLoad()

    collectionView.delegate = self

    collectionView.register(UINib.init(nibName: "Cell", bundle: nil), forCellWithReuseIdentifier: "Cell")
    if let flowLayout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
        flowLayout.estimatedItemSize = CGSize(width: 1,height: 1)
    }

    loadAPI(Page: 1) //display data

    scrollDownButton.clipsToBounds = true
    scrollDownButton.layer.cornerRadius = 15

    sendButton.addTarget(self, action: #selector(cvViewController.sendMessage), for: .touchDown) //push a new data

}

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

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    scheduledTimerWithTimeInterval()
    if move == 0{
        scrollToBottomAnimated(animated: true)
    }

    scrollDownButton.addTarget(self, action: #selector(cvchatViewController.scrollToBottomAnimated), for: .touchDown) //it will display last item on screen

    flowLayout.scrollDirection = .vertical

}

func scrollToBottomAnimated(animated: Bool) {
    guard self.collectionView.numberOfSections > 0 else{
        return
    }

    let items = self.collectionView.numberOfItems(inSection: 0)
    if items == 0 { return }

    let collectionViewContentHeight = self.collectionView.collectionViewLayout.collectionViewContentSize.height
    let isContentTooSmall: Bool = (collectionViewContentHeight < self.collectionView.bounds.size.height)

    if isContentTooSmall {
        self.collectionView.scrollRectToVisible(CGRect(x: 0, y: collectionViewContentHeight - 1, width: 1, height: 1), animated: animated)
        return
    }

    self.collectionView.scrollToItem(at: NSIndexPath(item: items - 1, section: 0) as IndexPath, at: .bottom, animated: animated)
}


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

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

     cell.vNameLabel.text = chatPages[indexPath.row].username
     cell.VCDateLabel.text = chatPages[indexPath.row].timeSent
     cell.vImageSend.image = UIImage(named: "1x1px")

    return cell
}


func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
    return true
}

有人能帮我解决这个问题吗?顺便说一下,我只是Swift的初学者。我很感激你的回答。谢谢

NB:我已经简化了代码,因为实际的代码非常复杂。