How to reload views on UIViewController on demand? - ios

Question

I have a UIViewController with some labels and a UICollectionView. A UICollectionView represents a self-made calendar, loaded from xib. When I tap on one of the collection view cells (say, choose a day in calendar), I change my underlying model accordingly, and I need the labels to update. But nothing gets updated on tap.
I have a method that updates the labels and call it in viewDidLoad(). After first loading all labels become nil, and declaring labels as 'var' and not as 'weak var' doesn't help. When calling some of the functions on viewController's self.view like layoutSubviews(), labels seem to exist, viewDidLoad() (and updateLabels()) gets called, but nothing changes on the screen.
I've tried to create (subclass) a UIView with labels using xib and programmatically, placed the labels directly in viewController, putting all the code in one place - same result.
setNeedsDisplay(), life cycle methods, removing-adding to superview - none of this worked for me. Am I doing something wrong or missing something important?
class ChallengeViewController: UIViewController {
var challenge = Challenge(title: Challenge.sampleTitle, startDate: Challenge.sampleStartDate, durationInDays: 40, checkIns: [Bool](repeating: true, count: 40), cheatDaysPlanned: 2, isActive: true, roundNumber: 1, pointsScored: 0)
#IBOutlet weak var titleLabel: UILabel!
#IBOutlet weak var calendarView: CalendarView!
#IBOutlet weak var statisticsView: ChallengeStatisticsView!
//contains labels that should be updated
override func viewDidLoad() {
super.viewDidLoad()
calendarView.challenge = challenge
calendarView.updateMonthAndYearLabels(for: challenge)
statisticsView.updateLabels()
titleLabel.text = challenge.title
}
}
class CalendarView: UIView {
var challenge: Challenge?
//other code here
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "calendarCell", for: indexPath) as! CalendarCollectionViewCell
collectionView.performBatchUpdates({
if let challenge = challenge {
cell.update(challenge: challenge)
let viewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ChallengeScreenViewController") as! ChallengeViewController
viewController.view.layoutSubviews()
viewController.challenge = challenge
viewController.updateLabels()
collectionView.reloadItems(at: [indexPath])
}
}, completion: nil)
}
}

Answer 1

You're creating a brand new view controller in your cell.update and it's never on the screen, which is why you're not seeing any updates. Not sure what your update method actually does anyway but it seems like just calling self.updateLabels() or self.statisticsView.updateLabels() should do the trick. Not sure which since you seem to have both.

Answer 2

Why are you reloading your VC?
When you click on a collectionViewCell, create a delegate-protocol to tell the VC to reload the labels with the datamodel.

Answer 3

Use cellForItem(at:) method to get the selected cell
To update the view in the current view controller, just call the update method. Do not create a new view controller.
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = collectionView.cellForItem(at: indexPath) as! CalendarCollectionViewCell
if let challenge = challenge {
cell.update(challenge: challenge)
collectionView.reloadItems(at: [indexPath])
self.updateLabels()
}
}

Answer 4

I didn't know that UIStoryboard(name:, bundle:).instantiateViewController(withIdentifier:) creates a brand new vc, that was the main mistake.
So I've decided to use Notification Center to make the controller respond to changes in model.
Everything works now.
class CalendarView: UIView {
var challenge: Challenge?
//other code here
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "calendarCell", for: indexPath) as! CalendarCollectionViewCell
collectionView.performBatchUpdates({
if let challenge = challenge {
cell.update(challenge: challenge)
// assigning a new value to calendarView's own variable, posting the notification
self.challenge = challenge
let name = Notification.Name("CellTapped")
NotificationCenter.default.post(name: name, object: nil)
collectionView.reloadItems(at: [indexPath])
}
}, completion: nil)
}
}
class ChallengeViewController: UIViewController {
var challenge = Challenge(title: Challenge.sampleTitle, startDate: Challenge.sampleStartDate, durationInDays: 40, checkIns: [Bool](repeating: true, count: 40), cheatDaysPlanned: 2, isActive: true, roundNumber: 1, pointsScored: 0)
#IBOutlet weak var titleLabel: UILabel!
#IBOutlet weak var calendarView: CalendarView!
#IBOutlet weak var statisticsView: ChallengeStatisticsView!
// taking the changed variable from calendarView when the notification is posted
#objc func updateAfterTap() {
if let calendarViewChallenge = calendarView.challenge {
self.challenge = calendarViewChallenge
statisticsView.updateLabels()
}
}
override func viewDidLoad() {
super.viewDidLoad()
calendarView.challenge = challenge
calendarView.updateMonthAndYearLabels(for: challenge)
statisticsView.updateLabels()
titleLabel.text = challenge.title
NotificationCenter.default.addObserver(self, selector: #selector(self.updateAfterTap), name: Notification.Name("CellTapped"), object: nil)
}
}