Download images from firebase to ios

viewcontroller.swift

override func viewWillAppear(_ animated: Bool) {

magsCollectionRef.getDocuments { (snapshot, error) in
    if let err = error {
        debugPrint("error fetching documents")
    }else{
        guard let snap = snapshot else { return }
        
        for document in snap.documents {
            let data = document.data()
            let title = data["title"] as? String ?? "no title"
            let periodicity = data["periodicity"] as? String ?? "no periodicity"


            let newMags = Mags(title: title, periodicity: periodicity)
            
            self.mags.append(newMags)
            
            
        }
           self.tableView.reloadData()
}