Countdown timer in table view cell shows different values after scrolling - ios

Question

The problem is described in title, but to be more specific here is a full picture.
I have a custom table view cell subclass with label inside it displaying the countdown timer. When there a small portion of timers it works fine, but with a lot of data I need to display timers far beyond the visible cells and when I scroll down fast and then scroll up fast, the timer values in cells start to show different values until a certain point in time, after which it shows the right value.
I tried different variants for those reuseable cells, but I can’t spot a problem. Help needed!!!
Here is the code of implementation of logic.
Custom cell subclass:
let calendar = Calendar.current
var timer: Timer?
var deadlineDate: Date? {
didSet {
updateTimeLabel()
}
}
override func awakeFromNib() {
purchaseCellCardView.layer.cornerRadius = 10
let selectedView = UIView(frame: CGRect.zero)
selectedView.backgroundColor = UIColor.clear
selectedBackgroundView = selectedView
}
override func prepareForReuse() {
super.prepareForReuse()
if timer != nil {
print("Invalidated!")
timer?.invalidate()
timer = nil
}
}
func configure(for purchase: Purchase) {
purchaseSubjectLabel.text = purchase.subject
startingPriceLabel.text = purchase.NMC
stageLabel.text = purchase.stage
fzImageView.image = purchase.fedLaw.contains("44") ? #imageLiteral(resourceName: "FZ44") : #imageLiteral(resourceName: "FZ223")
timeLabel.isHidden = purchase.stage == "Работа комиссии"
warningImageView.image = purchase.warningImage
}
func updateTimeLabel() {
setTimeLeft()
timer = Timer(timeInterval: 1, repeats: true) { [weak self] _ in
guard let strongSelf = self else {return}
strongSelf.setTimeLeft()
}
RunLoop.current.add(timer!, forMode: .commonModes)
}
#objc private func setTimeLeft() {
let currentDate = getCurrentLocalDate()
if deadlineDate?.compare(currentDate) == .orderedDescending {
var components = calendar.dateComponents([.day, .hour, .minute, .second], from: currentDate, to: deadlineDate!)
let dayText = (components.day! == 0 || components.day! < 0) ? "" : String(format: "%i", components.day!)
let hourText = (components.hour == 0 || components.hour! < 0) ? "" : String(format: "%i", components.hour!)
switch (dayText, hourText) {
case ("", ""):
timeLabel.text = String(format: "%02i", components.minute!) + ":" + String(format: "%02i", components.second!)
case ("", _):
timeLabel.text = hourText + " ч."
default:
timeLabel.text = dayText + " дн."
}
} else {
stageLabel.text = "Работа комиссии"
timeLabel.text = ""
timeLabel.isHidden = true
timer?.invalidate()
}
}
private func getCurrentLocalDate() -> Date {
var now = Date()
var nowComponents = calendar.dateComponents([.year, .month, .day, .hour, .minute, .second], from: now)
nowComponents.timeZone = TimeZone(abbreviation: "UTC")
now = calendar.date(from: nowComponents)!
return now
}
deinit {
print("DESTROYED")
timer?.invalidate()
timer = nil
}
The most important part of tableView(_cellForRowAt:)
case .results:
if filteredArrayOfPurchases.isEmpty {
let cell = tableView.dequeueReusableCell(
withIdentifier: TableViewCellIdentifiers.nothingFoundCell,
for: indexPath)
let label = cell.viewWithTag(110) as! UILabel
switch segmentedControl.index {
case 1:
label.text = "Нет закупок способом\n«Запрос предложений»"
case 2:
label.text = "Нет закупок способом\n«Конкурс»"
case 3:
label.text = "Нет закупок способом\n«Аукцион»"
default:
label.text = "Нет закупок способом\n«Запрос котировок»"
}
return cell
} else {
let cell = tableView.dequeueReusableCell(
withIdentifier: TableViewCellIdentifiers.purchaseCell,
for: indexPath) as! PurchaseCell
cell.containerViewTopConstraint.constant = indexPath.row == 0 ? 8.0 : 4.0
cell.containerViewBottomConstraint.constant = indexPath.row == filteredArrayOfPurchases.count - 1 ? 8.0 : 4.0
let purchase = filteredArrayOfPurchases[indexPath.row]
cell.configure(for: purchase)
if cell.timer != nil {
cell.updateTimeLabel()
} else {
search.getDeadlineDateAndTimeToApply(purchase.purchaseURL, purchase.fedLaw, purchase.stage, completion: { (date) in
cell.deadlineDate = date
})
}
return cell
}
And the last piece of a puzzle:
func getDeadlineDateAndTimeToApply(_ url: URL?, _ fedLaw: String, _ stage: String, completion: #escaping (Date) -> ()) {
var deadlineDateAndTimeToApply = Date()
guard stage != "Работа комиссии" else { return }
if let url = url {
dataTask = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
if let error = error as NSError?, error.code == -403 {
// TODO: Add alert here
return
}
guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200, let data = data, let html = String(data: data, encoding: .utf8), let purchasePageBody = try? SwiftSoup.parse(html), let purchaseCard = try? purchasePageBody.select("td").array() else {return}
let mappedArray = purchaseCard.map(){String(describing: $0)}
if fedLaw.contains("44") {
guard let deadlineDateToApplyString = try? purchaseCard[(mappedArray.index(of: "<td class=\"fontBoldTextTd\">Дата и время окончания подачи заявок</td>"))! + 1].text().components(separatedBy: " ") else {return}
dateFormatter.dateFormat = "dd.MM.yyyy HH:mm"
let deadlineDateToApply = deadlineDateToApplyString.first!
let deadlineTimeToApply = deadlineDateToApplyString[1]
guard let deadlineDateAndTimeToApplyCandidate = dateFormatter.date(from: "\(deadlineDateToApply) \(deadlineTimeToApply)") else {return}
deadlineDateAndTimeToApply = deadlineDateAndTimeToApplyCandidate
} else {
guard let deadlineDateToApplyString = try? purchaseCard[(mappedArray.index(of: "<td>Дата и время окончания подачи заявок<br> (по местному времени заказчика)</td>"))! + 1].text().components(separatedBy: " ") else {return}
dateFormatter.dateFormat = "dd.MM.yyyy HH:mm"
let deadlineDateToApply = deadlineDateToApplyString.first!
let deadlineTimeToApply = deadlineDateToApplyString[2]
guard let deadlineDateAndTimeToApplyCandidate = dateFormatter.date(from: "\(deadlineDateToApply) \(deadlineTimeToApply)") else {return}
deadlineDateAndTimeToApply = deadlineDateAndTimeToApplyCandidate
}
DispatchQueue.main.async {
completion(deadlineDateAndTimeToApply)
}
})
dataTask?.resume()
}
}
A few notes:
Tried resetting deadlineDate to nil in prepareForReuse() - doesn’t help;
Using SwiftSoup Framework to parse HTML as you can see in the last code example if it matters.

Answer 1

This is quite a lot of code but from what you are describing your issue is in reusing cells.
You would do well to separate the timers out of the cells and put them inside your objects. It is where they belong (or in some manager like view controller). Imagine having something like the following:
class MyObject {
var timeLeft: TimeInterval = 0.0 {
didSet {
if timeLeft > 0.0 && timer == nil {
timer = Timer.scheduled...
} else if timeLeft <= 0.0, let timer = timer {
timer.invalidate()
self.timer = nil
}
delegate?.myObject(self, updatedTimeLeft: timeLeft)
}
}
weak var delegate: MyObjectDelegate?
private var timer: Timer?
}
Now all you need is is a cell for row at index path to assign your object: cell.myObject = myObjects[indexPath.row].
And your cell would do something like:
var myObject: MyObject? {
didSet {
if oldValue.delegate == self {
oldValue.delegate = nil // detach from previous item
}
myObject.delegate = self
refreshUI()
}
}
func myObject(_ sender: MyObject, updatedTimeLeft timeLeft: TimeInterval) {
refreshUI()
}
I believe the rest should be pretty much straight forward...

Answer 2

Your problem is here:
search.getDeadlineDateAndTimeToApply(purchase.purchaseURL,
purchase.fedLaw,
purchase.stage,
completion: { (date) in
cell.deadlineDate = date
})
getDeadlineDateAndTimeToApply runs asynchronously, calculates something, and then updates the cell.deadlineData in the main thread (which is fine). But in the meantime, while calculating something, the user might have scrolled up and down, the cell might have been reused for another row, and now the update updates the cell incorrectly.
What you need to do is: Do not store the UITableViewCell directly. Instead, keep track of the IndexPath to be updated, and once the caluclation is done, retrieve the the cell that belongs to that IndexPath and update this.