pre select/highlight UICollectionViewCell on first load of view

Question

Im trying to preselect the first object/UICollectionViewCell in the UICollectionView? I have tried:

self.dateCollectionView.allowsMultipleSelection=NO;

[self.da         


        

Answer 1

For me, putting it in viewDidAppear: cause a second to select, so the user will see both states (i.e. not selected, and selected). To avoid this, I put it in viewWillAppear: instead and worked like a charm

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

Answer 2

In viewDidAppear:

NSIndexPath *indexPathForFirstRow = [NSIndexPath indexPathForRow:0 inSection:0];
[self.dateCollectionView selectItemAtIndexPath:indexPathForFirstRow animated:NO scrollPosition:UICollectionViewScrollPositionNone];
[self collectionView:self.dateCollectionView didSelectItemAtIndexPath:indexPathForFirstRow];

Answer 3

• Here is full code link

In my case. I solved it via subclass a UICollectionView class with Generic types

// ******************************************
//
// MARK: - Config injection, Extend whatever you want
//
// ******************************************
struct CCCollectionViewConfig {
    var itemSize: CGSize?
    var minimumInteritemSpacing: CGFloat?
    var minimumLineSpacing: CGFloat?
    var allowsDefaultSelection: Bool = true
}

// ******************************************
//
// MARK: - Generic CCCollectionView
//
// ******************************************
final class CCCollectionView<T, Cell: UICollectionViewCell>: UICollectionView, UICollectionViewDataSource, UICollectionViewDelegate {

    typealias SelectHandler = (T, IndexPath?) -> Void

    typealias CellConfigure = (Cell, T) -> Void

    var contents: [T] = [] {
        didSet {
            DispatchQueue.main.async {
                self.reloadData()
                self.selectedIndexPath = IndexPath(item: (self.config.allowsDefaultSelection) ? 0 : -1, section: 0)
            }
        }
    }

    var configure: CellConfigure

    var selectHandler: SelectHandler

    var selectedIndexPath: IndexPath

    private var config: CCCollectionViewConfig

    private let identifier = "identifier"

    init(contents: [T], config: CCCollectionViewConfig, configure: @escaping CellConfigure, selectHandler: @escaping SelectHandler) {

        self.config = config
        self.contents = contents
        self.configure = configure
        self.selectHandler = selectHandler
        self.selectedIndexPath = IndexPath(item: (config.allowsDefaultSelection) ? 0 : -1, section: 0)

        let layout = UICollectionViewFlowLayout()

        if let size = config.itemSize {
            layout.itemSize = size
        }

        layout.minimumInteritemSpacing = config.minimumInteritemSpacing ?? 0
        layout.minimumLineSpacing = config.minimumLineSpacing ?? 0
        layout.scrollDirection = .vertical
        layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)

        super.init(frame: .zero, collectionViewLayout: layout)

        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    private func setup() {
        register(Cell.self, forCellWithReuseIdentifier: identifier)

        super.delegate = self
        super.dataSource = self

        allowsMultipleSelection = false
        isScrollEnabled = false
        backgroundColor = .clear
    }

    // ******************************************
    //
    // MARK: - UICollectionViewDataSource, UICollectionViewDelegate
    //
    // ******************************************

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath) as! Cell
        cell.isSelected = (selectedIndexPath == indexPath)
        let content = contents[indexPath.row]
        configure(cell, content)
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

        let content = contents[indexPath.row]
        selectHandler(content, indexPath)

        /// If selected item is equal to current selected item, ignore it
        if selectedIndexPath == indexPath {
            return
        }

        /// Handle selected cell
        let selectedCell = collectionView.cellForItem(at: indexPath)
        selectedCell?.isSelected = true

        /// Handle deselected cell
        let deselectItem = collectionView.cellForItem(at: selectedIndexPath)
        deselectItem?.isSelected = false

        selectedIndexPath = indexPath
    }
}

// ******************************************
//
// MARK: - CollectionViewCell
//
// ******************************************
final class CCCollectionViewCell: UICollectionViewCell {

    var title: String = "" {
        didSet {
            titleLabel.text = title
        }
    }

    private let titleLabel: UILabel = {
        let label = UILabel()
        return label
    }()


    var _isSelected: Bool = false
    override var isSelected: Bool {
        get {
            return _isSelected
        }
        set(newValue) {
            _isSelected = newValue
            updateSelection()
        }
    }

    private func updateSelection() -> Void {
        contentView.layer.borderColor = isSelected ? UIColor.red.cgColor : UIColor.green.cgColor
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.addSubview(titleLabel)
        contentView.layer.cornerRadius = 2.0
        contentView.layer.borderWidth = 2.0
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Then use it inside your ViewController

private let fakeContents = Array(repeating: "123123", count: 40)

/// Collection View Config
private lazy var config: CCCollectionViewConfig = {
    return CCCollectionViewConfig(itemSize: CGSize(width: 100, height: 30),
                                  minimumInteritemSpacing: 4.0,
                                  minimumLineSpacing: 4.0)
}()

/// Collection View Config
private lazy var collectionView: CCCollectionView<String, CCCollectionViewCell> = {
    let cv = CCCollectionView<String, CCCollectionViewCell>(contents: fakeContents, config: config, configure: { (cell: CCCollectionViewCell, content) in
        cell.title = content
    }) { [weak self] (content, indexPath) in
        guard let self = self else { return }
        guard let row = indexPath?.row else { return }
    }
    return cv
}()