How to prevent tableView from crashing with asynchronous methods? - swift

Question

I am making a tableView with pictures inside it. The pictures are the profile pictures from people which can join, leave and make there own room. In that room, the tableView is displayed.
To save data, I want to store every profile picture in the documents directory when people are joining the room. Now that is working, but the tableView reloads to often even when I am calling it twice. Because it reloads to much, it crashes because the array is out of index.
The crash happens to be on the picture array, not the username array. This is my code (a bit much):
private var playersRefHandle: FIRDatabaseHandle?
var channelRef: FIRDatabaseReference?
var players = [String]()
var playerImages = [UIImage]()
var playerUIDs = [String]()
var playersImageVersion = [String]()
var channel: Channel? {
didSet {
title = channel?.name
}
}
override func viewDidLoad() {
super.viewDidLoad()
playersView.delegate = self
playersView.dataSource = self
let storage = FIRStorage.storage()
let storageRef = storage.reference(forURL: "gs://X-f5beb.appspot.com")
channelRef?.observeSingleEvent(of: .value, with: { (snapshot) in
if let snapDict = snapshot.value as? [String:AnyObject]{
for each in snapDict{
let UIDs = each.value["userID"] as? String
let pictureVersion = each.value["PictureVersion"] as? String
if let allUIDS = UIDs{
if let allPictureVersions = pictureVersion{
self.playerUIDs.append(UIDs!)
self.playersImageVersion.append(allPictureVersions)
let userNames = each.value["username"] as? String
if let users = userNames{
self.players.append(users)
}
if self.checkDataExist(dataToCheck: "\(UIDs!)" + "Image.png") == false || self.isCurrentImageVersionStored(pathToImage: "\(UIDs!)" + "ImageVersion.txt", playersVersionImage: "\(allPictureVersions)") == false
{
print("image needs to be downloaded online")
let profilePicRef = storageRef.child((allUIDS)+"/profile_picture.png")
profilePicRef.data(withMaxSize: 1 * 500 * 500) { data, error in
if let error = error {
}
if (data != nil)
{
let image = UIImage(data: data!)
let convertImage = UIImagePNGRepresentation(image!)
let pathUIDImage = self.getDocumentsDirectory().appendingPathComponent(allUIDS + "Image.png")
try? convertImage!.write(to: pathUIDImage)
let playersUIDImageVersion = allPictureVersions
var pathUIDImageVersion = self.getDocumentsDirectory().appendingPathComponent(allUIDS + "ImageVersion.txt")
try? playersUIDImageVersion.write(to: pathUIDImageVersion, atomically: true, encoding: .utf8)
self.playerImages.append(UIImage (data: data!)!)
}
}
}
else
{
self.playerImages.append(self.retrieveImageFromDocuments(playersUID: UIDs!))
}
}
}
}
}
self.playersView.reloadData()
self.observePlayers()
})
}
deinit {
if let refHandle = playersRefHandle {
channelRef?.removeObserver(withHandle: refHandle)
}
}
override func willMove(toParentViewController parent: UIViewController?)
{
if parent == nil
{
print("back")
}
}
func getDocumentsDirectory() -> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
let documentsDirectory = paths[0]
return documentsDirectory
}
func checkDataExist(dataToCheck: String) -> Bool
{
let documentsURL = try! FileManager().url(for: .documentDirectory,
in: .userDomainMask,
appropriateFor: nil,
create: true)
let file = documentsURL.appendingPathComponent(dataToCheck)
let fileExists = FileManager().fileExists(atPath: file.path)
if fileExists == true
{
return true
}
else
{
return false
}
}
func isCurrentImageVersionStored(pathToImage: String, playersVersionImage: String) -> Bool
{
if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {
let path = dir.appendingPathComponent(pathToImage)
do {
let currentStoredImage = try String(contentsOf: path, encoding: String.Encoding.utf8)
let currentStoredImageInt = Int(currentStoredImage)
let playersVersionImageInt = Int(playersVersionImage)
if currentStoredImageInt == playersVersionImageInt
{
return true
}
else
{
return false
}
}
catch {/* error handling here */}
return false
}
return false
}
func retrieveImageFromDocuments(playersUID: String) -> UIImage
{
print("image is available offline")
let nsDocumentDirectory = FileManager.SearchPathDirectory.documentDirectory
let nsUserDomainMask = FileManager.SearchPathDomainMask.userDomainMask
let paths = NSSearchPathForDirectoriesInDomains(nsDocumentDirectory, nsUserDomainMask, true)
let dirPath = paths.first
let imageURL = URL(fileURLWithPath: dirPath!).appendingPathComponent("\(playersUID)" + "Image.png")
let profileImageForUser = UIImage(contentsOfFile: imageURL.path)
return profileImageForUser!
}
func observePlayers()
{
playersRefHandle = channelRef?.child("username").observe(.childChanged, with: { (snapshot) -> Void in
print("added player")
})
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return players.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
print("configuring one of multiple cells")
print(playerImages.count)
print(players.count)
var cell = tableView.dequeueReusableCell(withIdentifier: "playersCell") as! PlayersCellInMultiplayer
cell.playersUsername?.text = players[indexPath.row] as String
cell.playersImage?.image = playerImages[indexPath.row] as UIImage
return cell
}
This is my print of a random channel with a few users in it:
image is available offline
image needs to be downloaded online
configuring one of multiple cells
1
2
configuring one of multiple cells
1
2
Why does this happen? Is this of asynchronous methods? What is the best way to fix it?