为什么 didSelect function 仅适用于视图 controller 中的两个集合视图之一？

Question

I have two collection views (restaurantCollectionView and filterCollectionView) and I want to update the restaurantCollectionView after selecting a filterCollectionView cell. I have tried to use didSelected function. However, it seems that the function always takes restaurantCollectionView, not filterCollectionView, as the input. How can I achieve filtering using these two collection views?

The following is my current code. I left out some irrelevant setup codes such as creating Restaurant and Filter objects.

class ViewController: UIViewController {

    var filterCollectionView: UICollectionView!
    var restaurantCollectionView: UICollectionView!

    var filters = [Filter]()

    var restaurants1 = [Restaurant]()
    var restaurants2 = [Restaurant]()

    override func viewDidLoad() {
        super.viewDidLoad()

        title = "My Restaurants"
        view.backgroundColor = .lightGray
        navigationController?.navigationBar.barTintColor = UIColor(displayP3Red: 0.2, green: 0.3, blue: 0.8, alpha: 0.7)
        navigationController?.navigationBar.titleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.white]

        filters = [mexican, american, asian, greek, fastfood, seafood, breakast, lunch, dinner, cheap, acceptable]
        restaurants1 = [chipotle, chick, pokeland, ctb, fourseasons, aladdins]
        restaurants2 = [chipotle, chick, pokeland, ctb, fourseasons, aladdins]

        let filterLayout = UICollectionViewFlowLayout()
        filterLayout.scrollDirection = .horizontal
        filterLayout.minimumInteritemSpacing = padding
        filterLayout.minimumLineSpacing = padding

        let restaurantLayout = UICollectionViewFlowLayout()
        restaurantLayout.scrollDirection = .vertical
        restaurantLayout.minimumInteritemSpacing = 5
        restaurantLayout.minimumLineSpacing = padding

        filterCollectionView = UICollectionView(frame: .zero, collectionViewLayout: filterLayout)
        filterCollectionView.translatesAutoresizingMaskIntoConstraints = false
        filterCollectionView.backgroundColor = .lightGray
        filterCollectionView.register(FilterCollectionViewCell.self, forCellWithReuseIdentifier: filterReuseIdentifier)
        filterCollectionView.dataSource = self
        filterCollectionView.delegate = self
        view.addSubview(filterCollectionView)

        restaurantCollectionView = UICollectionView(frame: .zero, collectionViewLayout: restaurantLayout)
        restaurantCollectionView.translatesAutoresizingMaskIntoConstraints = false
        restaurantCollectionView.backgroundColor = .lightGray
        restaurantCollectionView.register(RestaurantCollectionViewCell.self, forCellWithReuseIdentifier: restaurantReuseIdentifier)
        restaurantCollectionView.dataSource = self
        restaurantCollectionView.delegate = self
        view.addSubview(restaurantCollectionView)


        setupConstraints()

    }

    func setupConstraints() {

        NSLayoutConstraint.activate([
            filterCollectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 2),
            filterCollectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: padding),
            filterCollectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -padding),
            filterCollectionView.heightAnchor.constraint(equalToConstant: 70)
        ])

        NSLayoutConstraint.activate([
            restaurantCollectionView.topAnchor.constraint(equalTo: filterCollectionView.bottomAnchor, constant: 2),
            restaurantCollectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10),
            restaurantCollectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            restaurantCollectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10)
        ])
    }

}

extension ViewController: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        if collectionView == self.filterCollectionView{
            return filters.count
        }
        else {
            return restaurants2.count
        }
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        if collectionView == self.filterCollectionView {
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: filterReuseIdentifier, for: indexPath) as! FilterCollectionViewCell

            cell.backgroundColor = .white
            cell.filterName.setTitleColor(UIColor(displayP3Red: 0.2, green: 0.3, blue: 0.8, alpha: 0.7), for: .normal)
            cell.configure(filter: filters[indexPath.item])
            cell.filterName.addTarget(self, action: #selector(changeColor), for: .touchUpInside)
            return cell
        }
        else {
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: restaurantReuseIdentifier, for: indexPath) as! RestaurantCollectionViewCell

            cell.configure(restaurant: restaurants2[indexPath.item])
            return cell
        }
    }

    @objc func changeColor(sender: Any) {
        if let button = sender as? UIButton {
            let point: CGPoint = button.convert(.zero, to: filterCollectionView)
            if let indexPath = filterCollectionView.indexPathForItem(at: point) {
                let cell = filterCollectionView.cellForItem(at: indexPath) as! FilterCollectionViewCell
                if cell.backgroundColor == UIColor.white{
                    cell.backgroundColor = UIColor(displayP3Red: 0.2, green: 0.3, blue: 0.8, alpha: 0.7)
                    cell.filterName.setTitleColor(.white, for: .normal)
                }
                else {
                    cell.backgroundColor = UIColor.white
                    cell.filterName.setTitleColor(UIColor(displayP3Red: 0.2, green: 0.3, blue: 0.8, alpha: 0.7), for: .normal)
                }
            }
        }

    }

}

extension ViewController: UICollectionViewDelegateFlowLayout {

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        if collectionView == self.filterCollectionView{
            return CGSize(width: 100, height: 50)
        }
        else {
            let width = (collectionView.frame.width - 2 * padding) / 2.0
            let height = (collectionView.frame.height - 3 * padding) / 4.0
            return CGSize(width: width, height: height)
        }
    }

}

extension ViewController: UICollectionViewDelegate {

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        if collectionView == self.filterCollectionView {
            let requirement = filters[indexPath.item].filterName

            restaurants2 = restaurants1.filter({$0.cuisine.contains(requirement) || $0.time.contains(requirement) || $0.priceLevel == requirement})

            restaurantCollectionView.reloadData()
        }

    }

}

Answer 1

I can see you use a if statement in the delegate method to check whether the collection view is filterCollectionView . In that case with this code your filtering method would naturally not get called when the user selects a cell from the restaurantCollectionView because the if statement would return false.

With that being said, the collectionView:didSelectItemAtIndexPath: delegate method should get called on both collection views. Your delegates seem to be properly set up, and your view constraints seem correct as well. So if it doesn't get called, I would go ahead and start by checking whether you have any targets or gesture recognizers that would overlap with the cell's content view, and could possibly absorb the touches.

If you have any touch-related methods I would suggest you to first deactivate it and create a minimal project to make sure everything's working fine, and then capture the view hierarchy via the View Debugging tool in Xcode, it will pause your app and allow you to see your UI in 3D. From there you can easily see what is wrong.