View is calling viewDidLoad() when navigating back - ios

Question

When the user selects a cell in the collection view, it pushes to a new view controller for that cell.
The problem is that when the user swipes back, the collection view controller runs viewDidLoad() instead of viewDidAppear(). This causes the whole collection view to reload and go back up to the top (first cell) and the user has to scroll all the way back down to get to where they were before.
Does anyone know why this is happening??
import UIKit
import FirebaseStorage
class CollectionViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout {
let reuseIdentifier = "PostCell"
var post: [Post] = [Post]()
var imageURLs: [URL] = [URL]()
override func viewDidLoad() {
super.viewDidLoad()
self.navigationController?.hidesBarsOnSwipe = true
collectionView?.backgroundColor = UIColor(red: 0.91, green: 0.91, blue: 0.91, alpha: 1.00)
// Uncomment the following line to preserve selection between presentations
self.clearsSelectionOnViewWillAppear = false
// Register cell classes
collectionView?.register(PostCell.self, forCellWithReuseIdentifier: reuseIdentifier)
//setupHorizontalBar()
setupCollectionView()
// Get all of the posts
loadPosts()
print("loaded")
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
print("appeared")
collectionView.index
}
func setupCollectionView() {
if let layout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
layout.scrollDirection = .vertical
layout.minimumLineSpacing = 0
}
}
func loadPosts() {
postRef.observe(.value, with: { (snapshot) in
for eachPost in snapshot.value as! [String: Any] {
let dict: Dictionary<String, Any> = [eachPost.key: eachPost.value]
let post = Post(postDictionary: dict)
print(post)
self.posts.append(post)
self.collectionView?.reloadData()
}
})
}
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return posts.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! PostCell
//cell.backgroundColor = .brown
let post = posts[indexPath.row]
cell.nameLabel.text = post.name
let details = "\n\(post.address!)\n\n\(post.time!) \(post.date!)"
cell.postDetailTextView.text = details
if let imageURL = post.image {
print(imageURL)
cell.postImageView.sd_setImage(with: URL(string: imageURL))
}
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
let height = (self.view.frame.width - 20) * 9 / 16
return CGSize(width: self.view.frame.width, height: height + 5 + 140)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
When didSelectItemAt is called, I want the navigation controller to push to another view controller for the cell selected.
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print(indexPath)
let detailVC = DetailViewController()
self.navigationController?.pushViewController(detailVC, animated: true)
}
}