problem with adding element to swift array

Question

I am creating an application. I make a request to the firebase store, after that I add the result to the array, but in the end, when the array is displayed from viewDidLoad or other functions, I get an empty array. But if you make a conclusion immediately after the request, then everything is displayed correctly

`

import UIKit
import Firebase
import FirebaseStorage
import FirebaseFirestore


    
class CatalogVC: UIViewController {
   
    
    struct Item: Codable {
        var title: String
        var price: Int
        var description: String
        var imageUrl: String
    }
    
    @Published var items: [Item] = []
    
    let database = Firestore.firestore()
    
    @IBOutlet weak var textViewCatalog: UITextView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        let settings = FirestoreSettings()
        Firestore.firestore().settings = settings
        itemsList()
        print(items)
        showCatalogVC()
    }
    
    @IBAction func showCatalogTapped() {
        
    }
    
    private func showCatalogVC() {
        print("SHOW CATALOG")
        let storyboard = UIStoryboard(name:  "Main", bundle: nil)
        let dvc = storyboard.instantiateViewController(withIdentifier: "CatalogVC") as! CatalogVC
        self.present(dvc, animated: true, completion: nil)
    }
    
    func itemsList(){
        database.collection("catalog")
            .getDocuments { (snapshot, error) in
                self.items.removeAll()
                
                if let snapshot {
                    for document in snapshot.documents{
                        let docData = document.data()
                        let title: String = docData["title"] as? String ?? ""
                        let imageUrl: String = docData["imageUrl"] as? String ?? ""
                        let description: String = docData["description"] as? String ?? ""
                        let price: Int = docData["price"] as? Int ?? 0
                        
                        let item: Item = Item(title: title, price: price, description: description, imageUrl: imageUrl)
                        
                        self.items.append(item)
                    }
                }
                
            }
    }
    

}

`

I am creating an application. I make a request to the firebase store, after that I add the result to the array, but in the end, when the array is displayed from viewDidLoad or other functions, I get an empty array. But if you make a conclusion immediately after the request, then everything is displayed correctly

Firebase process is work in background thread and you are printing items in main thread.You are printing the items before the request completed. — Omer Tekbiyik
– Omer Tekbiyik, Commented Dec 13, 2022 at 12:41

CosmicTea · Accepted Answer · 2022-12-13 13:29:58Z

Getting data from Firebase is asynchronous process. So here you should make everything after loading data in closure database.collection("catalog").getDocuments {...}.

func itemsList(){
        database.collection("catalog")
            .getDocuments { (snapshot, error) in
                self.items.removeAll()
                
                if let snapshot {
                    for document in snapshot.documents{
                        let docData = document.data()
                        let title: String = docData["title"] as? String ?? ""
                        let imageUrl: String = docData["imageUrl"] as? String ?? ""
                        let description: String = docData["description"] as? String ?? ""
                        let price: Int = docData["price"] as? Int ?? 0
                        
                        let item: Item = Item(title: title, price: price, description: description, imageUrl: imageUrl)
                        
                        self.items.append(item)
                    }
                }
                print(self.items) //print items to see them
                //here use items data
                
            }
    }

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