Firebase observeSingleEvent continuously duplicate entry being appended in my array - swift

Question

When I refresh the collection view the data duplicates by +1 in my. How can I avoid duplicate entries in my array when I pull to refresh this function?
Also used self.posts.removeAll() still no result.
var posts = [Post]() {
didSet {
collectionView?.reloadData()
}
}
var following = [String]()
let refreshControl = UIRefreshControl()
override func viewDidLoad() {
super.viewDidLoad()
refreshControl.tintColor = UIColor.gray
refreshControl.addTarget(self, action: #selector(fetchPosts), for: UIControlEvents.valueChanged)
collectionView?.addSubview(refreshControl)
collectionView?.alwaysBounceVertical = true
fetchPosts()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.collectionView.reloadData()
}
func fetchPosts(){
let ref = FIRDatabase.database().reference()
ref.child("users").queryOrderedByKey().observeSingleEvent(of: .value, with: { snapshot in
guard let users = snapshot.value as? [String : AnyObject] else {
return
}
print(snapshot.key)
for (_,value) in users {
if let uid = value["uid"] as? String {
if uid == FIRAuth.auth()?.currentUser?.uid {
if let followingUsers = value["following"] as? [String : String]{
for (_,user) in followingUsers{
self.following.append(user)
print(user)
}
}
self.following.append(FIRAuth.auth()!.currentUser!.uid)
ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in
for postSnapshot in snap.children.allObjects as! [FIRDataSnapshot] {
let post = postSnapshot.value as! [String : AnyObject]
print(snap.key)
if let userID = post["userID"] as? String {
for each in self.following {
if each == userID {
print(each)
let posst = Post()
if let date = post["date"] as? Int, let author = post["author"] as? String, let likes = post["likes"] as? Int, let pathToImage = post["pathToImage"] as? String, let postID = post["postID"] as? String {
posst.date = Int(date)
posst.author = author
posst.likes = likes
posst.pathToImage = pathToImage
posst.postID = postID
posst.userID = userID
print(posst)
if let people = post["peopleWhoLike"] as? [String : AnyObject] {
for (_,person) in people {
posst.peopleWhoLike.append(person as! String)
}
}
var postExist:Bool = false
for post in self.posts {
if post.postID == posst.postID {
postExist = true
break
}
}
if !postExist {
self.posts.append(posst)
}
self.posts.sort(by: {$0.date! > $1.date!})
self.refreshControl.endRefreshing()
}
}
}
self.collectionView.reloadData()
}
}
})
}
}
}
})
ref.removeAllObservers()
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return posts.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PostCell.identifier, for: indexPath) as! PostCell
cell.posts = posts[indexPath.row]
let post = posts[indexPath.row]
for person in post.peopleWhoLike {
if person == FIRAuth.auth()!.currentUser!.uid {
cell.like.isHidden = true
cell.unlike.isHidden = false
break
}
}
return cell
}
}
Updated with the solutions.

Answer 1

I take it that when the refresh is activated, this function is called and that all the posts are downloaded. For your duplicate problem, it seems that you keep on appending data to your posts array without removing the old data.
ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in
let postsSnap = snap.value as! [String : AnyObject]
self.posts.removeAll() // This will remove previously downloaded posts.
// All your other code ...