Passing data from a child VC back to a Collection View Cell

Question

I have two ViewController: MainVC, and ChildVC. The MainVC includes a CollectionView with 5 cell. Each of these cell segues to the ChildVC. On this ChildVC, you can select different items which increases (or decreases) a counter on the ChildVC (the counter just reads "## selected".)

Basically, I just want this counter data on the ChildVC to be passed back onto a label of the respective MainVC cell that was tapped. For example: If user taps the second cell on the MainVC, selects 13 items on the ChildVC, then returns back to the MainVC, there will be a "13" in a label on the second cell. Then if the user taps the first cell, selects 5 items on the ChildVC, then returns back to the MainVC, there will be a "5" in a label on the first cell along with the "13" on second cell.

My progress:

I have decided that delegation is an appropriate solution for my requirements, as delegation makes it easy to pass data to/from VC's. I need assistance in passing data BACK from a ChildVC TO a CollectionView Cell.

My questions:

• Along with the selected counter count (Int), what other information should be passed to and from within the protocol? (I wasn't sure if the indexPath should be passed, so that the data displays on the correct cell on the MainVC?)
• On the MainVC, should the data received from the protocol ChildVC be sent to the CollectionViewCell? or the MainVC cellForItemAt method?

Update:

I have some progress below. But it's not working as intended.

In the below code, I have created both the ViewController (MainVC) and ChildVC. In the Child VC, there is a UISlider to emulate the selected counter. I would like this counter data passed back to the respective MainVC CollectionView Cells. What's happening now is the MainVC CollectionView gets a new cell added once I change the value of the slider! The 'Clear All Animals' btn needs to "zero out" the slider data for all the cells, but I haven't gotten that far yet..

View Controller (MainVC in my question above)

class ViewController: UIViewController {

    var allAnimals = AnimalData.getAllAnimals()
    @IBOutlet weak var mainCV: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()
        mainCV.dataSource = self

    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "AnimalSegue" {
            let childVC = segue.destination as! ChildVC
            childVC.delegate = self

            if let indexPath = self.mainCV.indexPath(for: sender as! AnimalCollectionViewCell) {
                let animalData = self.allAnimals[indexPath.item]
                childVC.animal = animalData
                childVC.indexPath = indexPath
            }

            childVC.allIndexPaths = getAllIndexPaths()

        }
    }

    func getAllIndexPaths() -> [IndexPath] {
        var indexPaths: [IndexPath] = []

        for i in 0..<mainCV.numberOfSections {
            for j in 0..<mainCV.numberOfItems(inSection: i) {
                indexPaths.append(IndexPath(item: j, section: i))
            }
        }
        return indexPaths
    }

}


extension ViewController: DataDelegate {
    func zeroOut(for animalObject: AnimalModel, at indexPath: [IndexPath]) {
        print("ZERO OUT")
        self.mainCV.reloadData()
    }

    func updatedData(for animalObject: AnimalModel, at indexPath: IndexPath ) {
        self.allAnimals[indexPath.item] = animalObject
        self.mainCV.reloadItems(at: [indexPath])
    }
}

extension ViewController: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return allAnimals.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "AnimalCell", for: indexPath as IndexPath) as! AnimalCollectionViewCell
        let animal = allAnimals[indexPath.item]

        cell.animal = animal

        return cell
    }
}

ChildVC

class ChildVC: UIViewController {


    @IBOutlet weak var animalTitleLabel: UILabel!
    @IBOutlet weak var labelCounter: UILabel!
    @IBOutlet weak var sliderLabel: UISlider!

    var delegate: DataDelegate?
    var animal: AnimalModel?
    var indexPath: IndexPath?
    var allIndexPaths: [IndexPath]?

    override func viewDidLoad() {
        super.viewDidLoad()
        animalTitleLabel.text = animal?.name
        animalTitleLabel.textColor = animal?.color ?? .white
        sliderLabel.value = Float(animal?.amountCounter ?? 0)
        self.labelCounter.text = "\(Int(sliderLabel.value))"

    }

    @IBAction func closeButtonPressed(_ sender: UIButton) {
        if let delegate = self.delegate,
            let indexPath = self.indexPath,
            let animal = self.animal {
            delegate.updatedData(for: animal, at: indexPath)
        }
        self.dismiss(animated: true, completion: nil)
    }


    @IBAction func sliderChanged(_ sender: UISlider) {
        let newValue = Int(sender.value)
        labelCounter.text = "\(newValue)"
        self.animal?.amountCounter = newValue
    }

    @IBAction func clearAllBtnPressed(_ sender: UIButton) {
        if let delegate = self.delegate,
            let all = self.allIndexPaths,
            var animal = self.animal {
            animal.amountCounter = 0
            delegate.zeroOut(for: animal, at: all)
        }
        self.dismiss(animated: true, completion: nil)
    }
}

Animal Collection View Cell

class AnimalCollectionViewCell: UICollectionViewCell {

    @IBOutlet weak var animalLabel: UILabel!
    @IBOutlet weak var counterLabel: UILabel!

    var animal: AnimalModel! {
        didSet {
            self.updateUI()
        }
    }

    func updateUI() {
        animalLabel.text = animal.name
        counterLabel.text = "\(animal.amountCounter)"
        self.backgroundColor = animal.color
    }

}

Data

struct AnimalData {
    static func getAllAnimals() -> [AnimalModel] {
        return [
            AnimalModel(name: "Cats", amountCounter: 0, color: UIColor.red),
            AnimalModel(name: "Dogs", amountCounter: 0, color: UIColor.blue),
            AnimalModel(name: "Fish", amountCounter: 0, color: UIColor.green),
            AnimalModel(name: "Goats", amountCounter: 0, color: UIColor.yellow),
            AnimalModel(name: "Lizards", amountCounter: 0, color: UIColor.cyan),
            AnimalModel(name: "Birds", amountCounter: 0, color: UIColor.purple)
        ]
    }
}

Delegate

protocol DataDelegate {
    func updatedData(for animalObject: AnimalModel, at: IndexPath)
    func zeroOut(for animalObject: AnimalModel, at: [IndexPath])
}

Screenshots below of what is happening. See how Dogs is being added as another cell with the value of 23? What should happen is the 0 should change to a 23 on the second blue Dogs cell. I don't understand updating the data source and reloading the correct cells??

How do i simply pass back the slider data into the cell that was originally tapped?

Any help is appreciated

Answer 1

You have the right idea with your delegation, but you need to be able to provide context back to your delegate; ie. what animal was being updated? To do this, either MainVC needs to keep a property of the item that is being updated, or this information needs to be provided to the ChildVC so that it can provide the information back to the MainVC. I will use the latter approach.

Protocol

protocol DataDelegate {
    func updatedData(for animalObject: AnimalModel, at: IndexPath)
    func clearAll()
}

MainVC

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "AnimalSegue" {

        let childVC = segue.destination as! ChildVC
        childVC.delegate = self

        if let indexPath = self.mainCV.indexPath(for: sender as! AnimalCollectionViewCell) {
            let animalData = self.allAnimals[indexPath.item]
            childVC.animal = animalData
            childVC.indexPath = indexPath
        }

    }
}

extension ViewController: DataDelegate {
    func updatedData(for animalObject: AnimalModel, at indexPath: IndexPath ) {
        self.allAnimals[indexPath.item] = animalObject            
        self.mainCV.reloadItems(at: [indexPath])
    }

    func clearAll() {
       for index in 0..<self.allAnimals.count {
          self.allAnimals[index].count =0
       }
       self.mainCV.reloadData()
}

ChildVC

class ChildVC: UIViewController {


    @IBOutlet weak var animalTitleLabel: UILabel!
    @IBOutlet weak var labelCounter: UILabel!
    @IBOutlet weak var sliderLabel: UISlider!

    var delegate: DataDelegate?  
    var animal: AnimalModel? 
    var indexPath: IndexPath?

    override func viewDidLoad() {
        super.viewDidLoad()

        animalTitleLabel.text = animal?.name
        animalTitleLabel.textColor = animal?.color ?? .white
        sliderLabel.value = animal?.count ?? 0
        self.labelCounter.text = "\(Int(sliderLabel.value))"

    }

    @IBAction func closeButtonPressed(_ sender: UIButton) {
        if let delegate = self.delegate, 
           let indexPath = self.indexPath,
           let animal = self.animal {
            delegate.updatedData(for: animal, at: indexPath)
        }
        self.dismiss(animated: true, completion: nil)
    }


    @IBAction func sliderChanged(_ sender: UISlider) {
        let newValue = Int(sender.value)
        labelCounter.text = "\(newValue)"
        self.animal.count = newValue
    }

    @IBAction func clearAllBtnPressed(_ sender: UIButton) {
        delegate.clearAll()
    }

}

Updated

I have updated my answer to show how you could implement the clear all. In this case there is no reason to have the ChildVC update the data model; it simply needs to invoke a delegate method to let the MainVC know that it should update the model and refresh the collection view.

I think that this gives a hint as to why the ChildVC is the wrong place for the "clear all" button; if the code feels a bit clunky then the user experience may be a bit clunky too. The clear all button should just be on your MainVC - it doesn't make sense for a button on a animal-specific view to be affecting other animals. It also isn't "discoverable"; I don't find out about the clear all until I select an animal. I realise that this is just a "learning app" but user experience is an important part of iOS app development and so it is never too early to consider it; it can also impact the way you design your code as you can see here.

Answer 2

So this is a very incomplete display, but i believe this solution is something that you are lookin for

class mainVC {

    var counters: [Int] = [0,0,0,0,0]


    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(forIndexPath: indexPath) as CustomCell
        cell.counterLabel = counters[indexPath.item]
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let childVC =  ChildVC()
        childVC.finishedSelecting = { counter in
            self.counters.insert(counter, at: indexPath.item)
            childVC.dismiss()
            self.theCollectionView.reloadItems(at: [indexPath])
            //Or
            self.theCollectionView.reloadData()
        }

         present(childVC, animated: true)

    }
}

class childVC {

    var finishedSelecting: ((Int) -> ())?
    var counter = 5
    @objc func finishedButtonPressed() {
        finishedSelecting?(counter)

    }

    func count() {
        counter+=1
    }
}