Swift Firebase persistence - ios

Question

I'm trying to enable Firebase Persistence but my code keeps crashing with:
terminating with uncaught exception of type NSException
I have tried the line of code under my viewDidLoad as well as under DataService but I still get the same crash. what do I need to do to resolve this problem I'm facing
import UIKit
import Firebase
class HomeTeamSelectionVC: UIViewController, UITableViewDataSource, UITableViewDelegate {
#IBOutlet weak var tableView: UITableView!
var club: Clubs!
var player = [Players]()
var playerFirstName = String()
var playerLastName = String()
var playerSelected: Bool = false
override func viewDidLoad() {
super.viewDidLoad()
FIRDatabase.database().persistenceEnabled = true //Correct use of????
CLUB_KEY = ""
CLUB_KEY = club.clubKey
tableView.dataSource = self
tableView.delegate = self
DataService.ds.REF_PLAYERS.queryOrdered(byChild: "clubKey").queryEqual(toValue: club.clubKey).observe(.value, with: { (snapshot) in
print("PLAYERS_COUNT: \(snapshot.childrenCount)")
print("PLAYERS_SNAPSHOT: \(snapshot)")
self.player = []
if let snapshots = snapshot.children.allObjects as? [FIRDataSnapshot] {
for snap in snapshots {
if let playerDict = snap.value as? Dictionary<String, AnyObject> {
let key = snap.key
let players = Players(playerKey: key, dictionary: playerDict)
self.player.append(players)
}
}
}
// self.tableView.reloadData()
}) { (error) in
print(error.localizedDescription)
print("CHET: local error")
}
}
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return player.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let players = player[indexPath.row]
if let cell = tableView.dequeueReusableCell(withIdentifier: "HomeTeamPlayersCell") as? HomeTeamPlayersCell {
cell.configureCell(players)
return cell
} else {
return HomeTeamPlayersCell()
}
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let players: Players!
players = player[indexPath.row]
print (players.playerKey)
print (players.playerFirstName)
print (players.playerLastName)
dismiss(animated: true, completion: nil)
}
}

Answer 1

From Firebase documentation for persistenceEnabled property:
Note that this property must be set before creating your first Database reference and only needs to be called once per application.
As such, the standard practice is to set it once in your AppDelegate class. For instance:
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
FIRApp.configure()
FIRDatabase.database().persistenceEnabled = true
...
return true
}