Observe call not updating dictionary value. Problem with async - ios

Question

I'm trying to get a list of images from my firebase database. Inside the observe method, if I print the number of posts it works correctly. If I print the number of posts outside the observe function, but still inside the fetchPosts() function, I get 0. If I print the number of posts after the fetchPosts() call (the function that uses observe), I get 0.
How can I save the values to my dictionary posts inside of this async call? I've tried completion and dispatch groups. I might not have implemented them correctly so if you see an easy way to do it then please help me out. Here is the code:
import UIKit
import SwiftUI
import Firebase
import FirebaseUI
import SwiftKeychainWrapper
class FeedViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource{
#IBOutlet weak var collectionview: UICollectionView!
//var posts = [Post]()
var posts1 = [String](){
didSet{
collectionview.reloadData()
}
}
var following = [String]()
//var posts1 = [String]()
var userStorage: StorageReference!
var ref : DatabaseReference!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
fetchPosts()
}
// func lengthyTask(completionHandler: (Int) -> Int)
// {
// let result = completionHandler(42)
// print(result)
// }
//
// lengthyTask(completionHandler: { number in
// print(number)
// return 101
// })
//
func fetchPosts() {
let uid = Auth.auth().currentUser!.uid
let ref = Database.database().reference().child("posts")
let uids = Database.database().reference().child("users")
uids.observe(DataEventType.value, with: { (snapshot) in
let dict = snapshot.value as! [String:NSDictionary]
for (_,value) in dict {
if let uid = value["uid"] as? String{
self.following.append(uid)
}
}
ref.observe(DataEventType.value, with: { (snapshot2) in
let dict2 = snapshot2.value as! [String:NSDictionary]
for(key, value) in dict{
for uid2 in self.following{
if (uid2 == key){
for (key2,value2) in value as! [String:String]{
//print(key2 + "this is key2")
if(key2 == "urlToImage"){
let urlimage = value2
//print(urlimage)
self.posts1.append(urlimage)
self.collectionview.reloadData()
print(self.posts1.count)
}
}
}
}
}
})
self.collectionview.reloadData()
})
//ref.removeAllObservers()
//uids.removeAllObservers()
print("before return")
print(self.posts1.count)
//return self.posts1
}
func numberOfSections(in collectionView: UICollectionView) ->Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return posts1.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PostCell", for: indexPath) as! PostCell
cell.postImage.sd_setImage(with: URL(string: posts1[indexPath.row]))
//creating the cell
//cell.postImage.downloadImage(from: self.posts[indexPath.row])
// let storageRef = Storage.storage().reference(forURL: self.posts[indexPath.row].pathToImage)
//
//
print("im trying")
//let stickitinme = URL(fileURLWithPath: posts1[0])
//cell.postImage.sd_setImage(with: stickitinme)
//cell.authorLabel.text = self.posts[indexPath.row].author
//cell.likeLabel.text = "\(self.posts[indexPath.row].likes) Likes"
return cell
}
#IBAction func signOutPressed(_sender: Any){
signOut()
self.performSegue(withIdentifier: "toSignIn", sender: nil)
}
#objc func signOut(){
KeychainWrapper.standard.removeObject(forKey:"uid")
do{
try Auth.auth().signOut()
} catch let signOutError as NSError{
print("Error signing out: %#", signOutError)
}
dismiss(animated: true, completion: nil)
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
// Get the new view controller using segue.destination.
// Pass the selected object to the new view controller.
}
*/
}

Answer 1

You need only a few slightly changes
Declare posts1 simply
var posts1 = [String]()
and remove the property observer didSet
Delete the line self.collectionview.reloadData() right after self.posts1.append(..
Move the last occurrence of self.collectionview.reloadData() one level up, wrap it in a DispatchQueue block to update the collection view on the main thread and delete the print lines after the outer closure
}
DispatchQueue.main.async {
self.collectionview.reloadData()
}
})
})
}
And there is a typo in the second closure. It must be
let dict2 = snapshot2.value as! [String:NSDictionary]
for(key, value) in dict2 {
Variable names with trailing indices are pretty error-prone, better would be for example userDict and postDict
Edit :
This is the code with the order of execution
override func viewDidLoad() {
super.viewDidLoad()
collectionview.dataSource = self
collectionview.delegate = self
// 1
fetchPosts()
// 5
}
func fetchPosts() {
// 2
let uid = Auth.auth().currentUser!.uid
let ref = Database.database().reference().child("posts")
let uids = Database.database().reference().child("users")
// 3
uids.observe(DataEventType.value, with: { (snapshot) in
// 6
let dict = snapshot.value as! [String:NSDictionary]
for (_,value) in dict {
if let uid = value["uid"] as? String{
self.following.append(uid)
}
}
// 7
ref.observe(DataEventType.value, with: { (snapshot2) in
// 9
let dict2 = snapshot2.value as! [String:NSDictionary]
for(key, value) in dict2 { // TYPO!!!!
for uid2 in self.following{
if (uid2 == key){
for (key2,value2) in value as! [String:String]{
//print(key2 + "this is key2")
if(key2 == "urlToImage"){
let urlimage = value2
//print(urlimage)
self.posts1.append(urlimage)
print(self.posts1.count)
}
}
}
}
}
DispatchQueue.main.async {
// 11
self.collectionview.reloadData()
}
// 10
})
// 8
})
// 4
}