Adding Multiple Countdown Timers to UICollectionView - ios

Question

My goal is to have a unique (hh:mm:ss) countdown timer for each populated uicollectionviewcell within a uicollectionview.
Below is the (abbreviated) code I've been able to compile, but am stuck on getting it to really work in any capacity...any guidance would be appreciated.
class VC: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {
var timer = Timer()
var secondsRemaining: Int?
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath as IndexPath) as! ExampleCollectionViewCell
let expirationDate = Calendar.current.date(byAdding: .hour, value: 24, to: startDate)
secondsRemaining = expirationDate?.seconds(from: startDate)
timer = Timer(timeInterval: 1, target: self, selector: #selector(countdown), userInfo: nil, repeats: true)
return cell
}
#objc func countdown() {
secondsRemaining = secondsRemaining! - 1
if secondsRemaining == 0 {
print("CELL TIME HAS EXPIRED!")
timer.invalidate()
} else {
let hours = secondsRemaining! / 3600
let minutes = (secondsRemaining! % 3600) / 60
let seconds = (secondsRemaining! % 3600) % 60
let countdownLabelString = String(format: "%02d:%02d:%02d", hours, minutes, seconds)
//i need to take this countdownLabelString and set it to the
//countdownLabel.text that is an element of each cell. i tried
//doing all of this in the cell subclass, but no luck...
}
}
}

Answer 1

Collection view cells are not made to update constantly. If you want them to update, you have to tell them to update.
If you want each cell to show a different amount of time remaining, you need a data model that saves a separate expirationDate for each indexPath you display. If your collection view is a simple one-dimensional list of items, like a table view, then you could just use a 1-dimensional array. If your collection view shows a grid of cells you might need a 2 dimensional array of model objects.
Each time you add an item to your data model, include an expirationDate value. (The Date when that item expires.)
Then have your timer call the collection view's reloadData method each time it fires.
In your collectionView(collectionView:cellForItemAt:) method, use the indexPath to figure out which item in your data model you are displaying. Look up the expirationDate for that indexPath, calculate the time remaining from now until your expiration date, and display that information in the cell. (Use the Calendar method dateComponents(_:from:to:) to calculate the number of hours, minutes, and seconds between now and your expiration date.)
EDIT
DO NOT decrement a counter every time your timer fires. Do math on the difference between your expiration date and the current date using dateComponents(_:from:to:)
EDIT #2:
A sample collection view controller that does something like what you want is below:
import UIKit
private let reuseIdentifier = "aCell"
class DatesCollectionVC: UICollectionViewController {
weak var timer: Timer?
var dates: [Date] = []
lazy var componentsFormatter: DateComponentsFormatter = {
let formatter = DateComponentsFormatter()
formatter.allowedUnits = [.hour, .minute, .second]
return formatter
}()
override func viewDidLoad() {
super.viewDidLoad()
for _ in 1...100 {
let interval = Double(arc4random_uniform( 10000)) + 120
dates.append(Date().addingTimeInterval(interval))
}
timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in
self.collectionView?.reloadData()
}
}
// MARK: - UICollectionViewDataSource
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return dates.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as? MyCell else {
return UICollectionViewCell()
}
let now = Date()
let expireDate = dates[indexPath.row]
guard expireDate > now else {
cell.intervalLabel.text = "00"
return cell
}
let desiredComponents: Set<Calendar.Component> = [.hour, .minute, .second]
let components = Calendar.current.dateComponents(desiredComponents, from: now, to: expireDate)
cell.intervalLabel.text = self.componentsFormatter.string(from: components)
return cell
}
}
The code above looks like this: