Set default cell in a UICollectionView (SWIFT)?

Question

I'm a Swift beginner trying to implement a way to set a default cell in a CollectionView when the app first launches. I have overriden my 'isSelected' method to graphically show on the screen the selected cell eg; borderColor, etc...

My approach (rightly or not) so far is to call the 'didSelectItemAt' method inside my 'viewDidAppear' method.

I understand that the 'didSelectItemAt' method expects a CollectionView as its first argument, but not matter what I put as the first argument when I call the method inside my 'viewDidAppear' nothing seems to work.

any ideas?

extension DrinkMenuViewController: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return imageArray.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "DrinkTypeImageCollectionViewCell", for: indexPath) as! DrinkTypeImageCollectionViewCell

        cell.imgDrinkType.image = imageArray[indexPath.row]
        cell.lbDrinkType.text = drinkTypeArray[indexPath.row]

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "DrinkTypeImageCollectionViewCell", for: indexPath) as! DrinkTypeImageCollectionViewCell

        cell.isSelected = true

        print("selected cell: ", indexPath)
    }

    override func viewDidAppear(_ animated: Bool) {
        let indexPathForFirstRow = IndexPath(row: 0, section: 0)

        collectionView(<#T##collectionView: UICollectionView##UICollectionView#>, didSelectItemAt: indexPathForFirstRow)

        print (indexPathForFirstRow)
    }
}

Answer 1

You are not the one to explicitly call the delegate methods of any API.

func collectionView(_:didSelectItemAt:) is the delegate method of UICollectionView . The api itself handles when to call this method. So you must not call this method from anywhere in your code.

Again your implementation of func collectionView(_:didSelectItemAt:) doesn't make any sense. This method will automatically be called when you tap on any of your cell. You don't have to deque your cell again here.

Answer 2

You are probably asking for: pre select/highlight UICollectionViewCell on first load of view

Try this:

override func viewWillAppear(_ animated: Bool) {
let selectedIndexPath = IndexPath(item: 0, section: 0)
    collectionView.selectItem(at: selectedIndexPath, animated: false, scrollPosition: .left)
}