ios - アプリの最初の起動時に写真が表示されないのはなぜですか?

Question

携帯電話に保存されているユーザーのフォト アルバムの写真を保持するviewControllerを含むを実装しました。collectionViewアプリがユーザーに写真へのアクセス許可を求めた後のアプリの最初の起動時に、写真がcollectionView. しかし、アプリを終了して再起動すると、写真は正常に表示されます。

viewController以下は問題のコードです

import UIKit
import Photos

class ViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDelegateFlowLayout,UICollectionViewDataSource {

    var imageArray:[UIImage] = [UIImage]()

    var collectionView:UICollectionView! = {
        let layout = UICollectionViewFlowLayout()
        layout.minimumInteritemSpacing = 1
        layout.minimumLineSpacing = 1
        layout.scrollDirection = .vertical
        let CV = UICollectionView(frame: UIScreen.main.bounds, collectionViewLayout: layout)
        CV.translatesAutoresizingMaskIntoConstraints = false
        return CV
    }()

    var fetchResult: PHFetchResult<PHAsset> = PHFetchResult()

    override func viewDidLoad() {
        super.viewDidLoad()
        self.collectionView.delegate = self
        self.collectionView.dataSource = self
        collectionView.register(customPhotoCell.self, forCellWithReuseIdentifier: "Cell")
        self.view.addSubview(collectionView)
        setUpLayout()
        fetchAssets()
    }

    func setUpLayout(){
        collectionView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 50).isActive = true
        collectionView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: 0).isActive = true
        collectionView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: 0).isActive = true
        collectionView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 0).isActive = true
    }

    func fetchAssets(){
        let fetchOptions = PHFetchOptions()
        fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
        fetchResult = PHAsset.fetchAssets(with: .image, options: fetchOptions)
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! customPhotoCell
        let imageView = cell.imgView
        let requestOptions = PHImageRequestOptions()
        requestOptions.isSynchronous = true
        requestOptions.deliveryMode = .highQualityFormat
        PHImageManager.default().requestImage(for: fetchResult.object(at: indexPath.item) , targetSize: CGSize(width: 200,height: 200), contentMode: .aspectFill, options: requestOptions, resultHandler: {
            image,error in
            if let error = error{
                print(error)
            }
            self.imageArray.append(image!)
            imageView.image = image!
        })
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let width = self.view.bounds.width/3 - 1
        return CGSize(width: width, height: width)
    }

}

class customPhotoCell:UICollectionViewCell{

    var imgView:UIImageView = {
        let imgV = UIImageView()
        imgV.backgroundColor = .orange
        imgV.translatesAutoresizingMaskIntoConstraints = false
        return imgV
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.addSubview(imgView)
        imgView.topAnchor.constraint(equalTo: self.topAnchor, constant: 0).isActive = true
        imgView.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: 0).isActive = true
        imgView.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 0).isActive = true
        imgView.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: 0).isActive = true
    }
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

extension UIImageView{
    func fetchImage(asset: PHAsset, contentMode: PHImageContentMode, targetSize: CGSize) {
        let options = PHImageRequestOptions()
        options.version = .original
        PHImageManager.default().requestImage(for: asset, targetSize: targetSize, contentMode: contentMode, options: options) { image, _ in
            guard let image = image else { return }
            switch contentMode {
            case .aspectFill:
                self.contentMode = .scaleAspectFill
            case .aspectFit:
                self.contentMode = .scaleAspectFit
            }
            self.image = image
        }
    }
}

extension UIImage{
    func resizeImageWith() -> UIImage {
        let aspectRatio = CGFloat(self.size.width / self.size.height)
        let newWidth = UIScreen.main.bounds.width
        let newSize = CGSize(width: newWidth, height: newWidth/aspectRatio)
        UIGraphicsBeginImageContextWithOptions(newSize, true, 0)
        self.draw(in: CGRect(origin: CGPoint(x: 0, y: 0), size: newSize))
        let  newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!
    }
}