Swift 3 - iOS 11.2上的UICollectionview问题

Question

我有UICollectionView的两个问题。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。但是当我尝试使用iOS 11.2的设备时，我遇到了UICollectionView的问题。当一个新数据出现时，它应该出现在底部（这就是我想要的并且已经在iOS 10.3上完成了）。但iOS 11.2使其在新数据出现时滚动到顶部。

问题2

然后我已经从Xcode 8迁移到Xcode 9.2，因为Xcode 8没有直接支持iOS 11.但现在在Xcode 9.2 iOS 11.2模拟器上，我无法清楚地滚动集合视图，然后在UIAppDelegate中使用Thread 1: signal SIGABRT.中断

只要我知道，每当我断开插座时，就会出现这种错误。但我很确定我的所有网点都已关联。

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
}

任何人都可以帮我解决这个问题吗？顺便说一下，我只是Swift的初学者。我感谢您的所有回复。谢谢！

注意：我简化了代码，因为实际的代码非常复杂。