UICollectionView-refreshing: getting each cell more than one time - firebase

Question

Hi I'm having the issue that after refreshing my collectionView I am getting each cell twice on
my view. And after refreshing a second time I am getting each cell 3 times. I am also getting this issue when presenting the view with a segue a second time.
How can I fix that?
Can someone help me?
Thank you in advance!!!
import UIKit
import Firebase
class FeedViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
private let refreshControl = UIRefreshControl()
#IBOutlet weak var collectionview: UICollectionView!
var posts = [Post]()
override func viewDidLoad() {
super.viewDidLoad()
collectionview.refreshControl = refreshControl
refreshControl.addTarget(self, action: #selector(refreshWeatherData(_:)), for: .valueChanged)
refreshControl.tintColor = UIColor(hex: "#F17D32")
}
#objc private func refreshData(_ sender: Any) {
fetchData()
posts.removeAll()
collectionview.reloadData()
}
private func fetchData() {
getPost()
self.refreshControl.endRefreshing()
}
func getPosts(){
let ref = Database.database().reference()
ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in
let postsSnap = snap.value as! [String : AnyObject]
for (_,post) in postsSnap {
let posst = Post()
if let author = post["author"] as? String, late date = post["date"], let postID = post["postID"] as? String, let userID = post["userID"] as? String {
posst.date = date
posst.author = author
posst.postID = postID
posst.userID = userID
self.posts.sort(by: {$0.postdateprog > $1.postdateprog})
self.posts.append(posst)
}
self.collectionview.reloadData()
}
})
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print(posts.count)
return self.posts.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "postCell", for: indexPath) as! PostCell
cell.authorlabel.text = self.posts[indexPath.row].author
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize
{
return CGSize(width: self.collectionview.frame.width / 2 - 20, height: self.collectionview.frame.width * 0.7)
}
}

Answer 1

Firebase functions are asynchronous and the code in the closure will be called after the synchronous code runs. In other words, you have this
fetchData()
posts.removeAll()
collectionview.reloadData()
but posts.removeAll() and collectionview.reloadData() will be called before the array is populated.
So here's a truncated overview of the order in which things should be called.
#objc private func refreshData(_ sender: Any) {
self.loadFirebaseData()
}
func loadFirebaseData() {
...
self.posts = []
for (_,post) in postsSnap {
self.posts.append(posst)
}
self.posts.sort(by: {$0.postdateprog > $1.postdateprog}
self.collectionview.reloadData()
}
Notice that I moved the sort and the reloadData outside of the for loop. There's no reason to call those functions over and over as the datasource is being populated. Do it after that task is complete.