Why does my segue not wait until completion handler finished? - swift

Question

I have a page based app, using RootViewController, ModelViewController, DataViewController, and a SearchViewController.
In my searchViewController, I search for an item and then add or remove that Item to an array which is contained in a Manager class(and UserDefaults), which the modelViewController uses to instantiate an instance of DataViewController with the correct information loaded using the dataObject. Depending on whether an Item was added or removed, I use a Bool to determine which segue was used, addCoin or removeCoin, so that the RootViewController(PageView) will show either the last page in the array, (when a page is added) or the first (when removed).
Everything was working fine until I ran into an error which I can not diagnose, the problem is that when I add a page, the app crashes, giving me a "unexpectadely found nil when unwrapping an optional value"
This appears to be the problem function, in the searchViewController 'self.performSegue(withIdentifier: "addCoin"' seems to be called instantly, even without the dispatchque:
#objc func addButtonAction(sender: UIButton!) {
print("Button tapped")
if Manager.shared.coins.contains(dataObject) {
Duplicate()
} else if Manager.shared.coins.count == 5 {
max()
} else {
Manager.shared.addCoin(coin: dataObject)
CGPrices.shared.getData(arr: true, completion: { (success) in
print(Manager.shared.coins)
DispatchQueue.main.async {
self.performSegue(withIdentifier: "addCoin", sender: self)
}
})
}
searchBar.text = ""
}
Meaning that In my DataViewController, this function will find nil:
func getIndex() {
let index = CGPrices.shared.coinData.index(where: { $0.id == dataObject })!
dataIndex = index
}
I can't find out why it does not wait for completion.
I also get this error about threads:
[Assert] Cannot be called with asCopy = NO on non-main thread.
which is why I try to do the push segue using dispatch que
Here is my searchViewController full code:
import UIKit
class SearchViewController: UIViewController, UISearchBarDelegate {
let selectionLabel = UILabel()
let searchBar = UISearchBar()
let addButton = UIButton()
let removeButton = UIButton()
var filteredObject: [String] = []
var dataObject = ""
var isSearching = false
//Add Button Action.
#objc func addButtonAction(sender: UIButton!) {
print("Button tapped")
if Manager.shared.coins.contains(dataObject) {
Duplicate()
} else if Manager.shared.coins.count == 5 {
max()
} else {
Manager.shared.addCoin(coin: dataObject)
CGPrices.shared.getData(arr: true, completion: { (success) in
print(Manager.shared.coins)
DispatchQueue.main.async {
self.performSegue(withIdentifier: "addCoin", sender: self)
}
})
}
searchBar.text = ""
}
//Remove button action.
#objc func removeButtonActon(sender: UIButton!) {
print("Button tapped")
if Manager.shared.coins.contains(dataObject) {
Duplicate()
} else if Manager.shared.coins.count == 5 {
max()
} else {
Manager.shared.removeCoin(coin: dataObject)
self.performSegue(withIdentifier: "addCoin", sender: self)
}
searchBar.text = ""
}
//Prepare for segue, pass removeCoinSegue Bool depending on remove or addCoin.
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "addCoin" {
if let destinationVC = segue.destination as? RootViewController {
destinationVC.addCoinSegue = true
}
} else if segue.identifier == "addCoin" {
if let destinationVC = segue.destination as? RootViewController {
destinationVC.addCoinSegue = false
}
}
}
//Remove button action.
#objc func removeButtonAction(sender: UIButton!) {
if Manager.shared.coins.count == 1 {
removeAlert()
} else {
Manager.shared.removeCoin(coin: dataObject)
print(Manager.shared.coins)
print(dataObject)
searchBar.text = ""
self.removeButton.isHidden = true
DispatchQueue.main.async {
self.performSegue(withIdentifier: "removeCoin", sender: self)
}
}
}
//Search/Filter the struct from CGNames, display both the Symbol and the Name but use the ID as dataObject.
func filterStructForSearchText(searchText: String, scope: String = "All") {
if !searchText.isEmpty {
isSearching = true
filteredObject = CGNames.shared.coinNameData.filter {
// if you need to search key and value and include partial matches
// $0.key.contains(searchText) || $0.value.contains(searchText)
// if you need to search caseInsensitively key and value and include partial matches
$0.name.range(of: searchText, options: .caseInsensitive) != nil || $0.symbol.range(of: searchText, options: .caseInsensitive) != nil
}
.map{ $0.id }
} else {
isSearching = false
print("NoText")
}
}
//Running filter function when text changes.
func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
filterStructForSearchText(searchText: searchText)
if isSearching == true && filteredObject.count > 0 {
addButton.isHidden = false
dataObject = filteredObject[0]
selectionLabel.text = dataObject
if Manager.shared.coins.contains(dataObject) {
removeButton.isHidden = false
addButton.isHidden = true
} else {
removeButton.isHidden = true
addButton.isHidden = false
}
} else {
addButton.isHidden = true
removeButton.isHidden = true
selectionLabel.text = "e.g. btc/bitcoin"
}
}
override func viewDidLoad() {
super.viewDidLoad()
//Setup the UI.
self.view.backgroundColor = .gray
setupView()
}
override func viewDidLayoutSubviews() {
}
//Hide keyboard
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
self.view.endEditing(true)
}
//Alerts
func removeAlert() {
let alertController = UIAlertController(title: "Can't Remove", message: "\(dataObject) can't be deleted, add another to delete \(dataObject)", preferredStyle: .alert)
alertController.addAction(UIAlertAction(title: "Okay", style: .default, handler: nil))
self.present(alertController, animated: true, completion: nil)
}
func Duplicate() {
let alertController = UIAlertController(title: "Duplicate", message: "\(dataObject) is already in your pages!", preferredStyle: .alert)
alertController.addAction(UIAlertAction(title: "Okay", style: .default, handler: nil))
self.present(alertController, animated: true, completion: nil)
}
func max() {
let alertController = UIAlertController(title: "Maximum Reached", message: "\(dataObject) can't be added, you have reached the maximum of 5 coins. Please delete a coin to add another.", preferredStyle: .alert)
alertController.addAction(UIAlertAction(title: "Okay", style: .default, handler: nil))
self.present(alertController, animated: true, completion: nil)
}
}
and here is the DataViewController
import UIKit
class DataViewController: UIViewController {
#IBOutlet weak var dataLabel: UILabel!
//Variables and Objects.
//The dataObject carries the chosen cryptocurrencies ID from the CoinGecko API to use to get the correct data to load on each object.
var dataObject = String()
//The DefaultCurrency (gbp, eur...) chosen by the user.
var defaultCurrency = ""
//The Currency Unit taken from the exchange section of the API.
var currencyUnit = CGExchange.shared.exchangeData[0].rates.gbp.unit
var secondaryUnit = CGExchange.shared.exchangeData[0].rates.eur.unit
var tertiaryUnit = CGExchange.shared.exchangeData[0].rates.usd.unit
//Index of the dataObject
var dataIndex = Int()
//Objects
let cryptoLabel = UILabel()
let cryptoIconImage = UIImageView()
let secondaryPriceLabel = UILabel()
let mainPriceLabel = UILabel()
let tertiaryPriceLabel = UILabel()
//Custom Fonts.
let customFont = UIFont(name: "AvenirNext-Heavy", size: UIFont.labelFontSize)
let secondFont = UIFont(name: "AvenirNext-BoldItalic" , size: UIFont.labelFontSize)
//Setup Functions
//Get the index of the dataObject
func getIndex() {
let index = CGPrices.shared.coinData.index(where: { $0.id == dataObject })!
dataIndex = index
}
//Label
func setupLabels() {
//cryptoLabel from dataObject as name.
cryptoLabel.text = CGPrices.shared.coinData[dataIndex].name
//Prices from btc Exchange rate.
let btcPrice = CGPrices.shared.coinData[dataIndex].current_price!
let dcExchangeRate = CGExchange.shared.exchangeData[0].rates.gbp.value
let secondaryExchangeRate = CGExchange.shared.exchangeData[0].rates.eur.value
let tertiaryExchangeRate = CGExchange.shared.exchangeData[0].rates.usd.value
let realPrice = (btcPrice * dcExchangeRate)
let secondaryPrice = (btcPrice * secondaryExchangeRate)
let tertiaryPrice = (btcPrice * tertiaryExchangeRate)
secondaryPriceLabel.text = "\(secondaryUnit)\(String((round(1000 * secondaryPrice) / 1000)))"
mainPriceLabel.text = "\(currencyUnit)\(String((round(1000 * realPrice) /1000)))"
tertiaryPriceLabel.text = "\(tertiaryUnit)\(String((round(1000 * tertiaryPrice) / 1000)))"
}
//Image
func getIcon() {
let chosenImage = CGPrices.shared.coinData[dataIndex].image
let remoteImageUrl = URL(string: chosenImage)
guard let url = remoteImageUrl else { return }
URLSession.shared.dataTask(with: url) { (data, response, err) in
guard let data = data else { return }
do {
DispatchQueue.main.async {
self.cryptoIconImage.image = UIImage(data: data)
}
}
}.resume()
}
override func viewDidLoad() {
super.viewDidLoad()
// for family in UIFont.familyNames.sorted() {
// let names = UIFont.fontNames(forFamilyName: family)
// print("Family: \(family) Font names: \(names)")
// }
// Do any additional setup after loading the view, typically from a nib.
self.setupLayout()
self.getIndex()
self.setupLabels()
self.getIcon()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.dataLabel!.text = dataObject
view.backgroundColor = .lightGray
}
}
Edit: CGPrices Class with getData method:
import Foundation
class CGPrices {
struct Coins: Decodable {
let id: String
let name: String
let symbol: String
let image: String
let current_price: Double?
let low_24h: Double?
//let price_change_24h: Double?
}
var coinData = [Coins]()
var defaultCurrency = ""
var coins = Manager.shared.coins
var coinsEncoded = ""
static let shared = CGPrices()
func encode() {
for i in 0..<coins.count {
coinsEncoded += coins[i]
if (i + 1) < coins.count { coinsEncoded += "%2C" }
}
print("encoded")
}
func getData(arr: Bool, completion: #escaping (Bool) -> ()) {
encode()
let urlJSON = "https://api.coingecko.com/api/v3/coins/markets?vs_currency=btc&ids=\(coinsEncoded)"
guard let url = URL(string: urlJSON) else { return }
URLSession.shared.dataTask(with: url) { (data, response, err) in
guard let data = data else { return }
do {
let coinsData = try JSONDecoder().decode([Coins].self, from: data)
self.coinData = coinsData
completion(arr)
} catch let jsonErr {
print("error serializing json: \(jsonErr)")
print(data)
}
}.resume()
}
func refresh(completion: () -> ()) {
defaultCurrency = UserDefaults.standard.string(forKey: "DefaultCurrency")!
completion()
}
}

Answer 1

I figured it out.
The problem was inside my getData method I was not updated the coins array:
var coinData = [Coins]()
var defaultCurrency = ""
var coins = Manager.shared.coins
var coinsEncoded = ""
static let shared = CGPrices()
func encode() {
for i in 0..<coins.count {
coinsEncoded += coins[i]
if (i+1)<coins.count { coinsEncoded+="%2C" }
}
print("encoded")
}
I needed to add this line in getData:
func getData(arr: Bool, completion: #escaping (Bool) -> ()) {
//Adding this line to update the array so that the URL is appended correctly.
coins = Manager.shared.coins
encode()
let urlJSON = "https://api.coingecko.com/api/v3/coins/markets?vs_currency=btc&ids=\(coinsEncoded)"
This would fix the finding nil in the DataViewController, but the app would still crash do to updating UI Elements on a background thread, as the segue was called inside the completion handler of the getData method. to fix this, I used DispatchQue.Main.Async on the segue inside the getData method in the addButton function, to ensure that everything is updated on the main thread, like so:
#objc func addButtonAction(sender: UIButton!) {
print("Button tapped")
if Manager.shared.coins.contains(dataObject) {
Duplicate()
} else if Manager.shared.coins.count == 5 {
max()
} else {
Manager.shared.addCoin(coin: dataObject)
print("starting")
CGPrices.shared.getData(arr: true) { (arr) in
print("complete")
print(CGPrices.shared.coinData)
//Here making sure it is updated on main thread.
DispatchQueue.main.async {
self.performSegue(withIdentifier: "addCoin", sender: self)
}
}
}
searchBar.text = ""
}
Thanks for all the comments as they helped me to figure this out, and I learned a lot in doing so. Hopefully this can help someone else in their thought process when debugging, as one can get so caught up in one area of a problem, and forget to take a step back and look to other areas.