selecting_multiple_items_with_a_two-finger_pan_gesture

gistfile1.txt

//https://developer.apple.com/documentation/uikit/uitableviewdelegate/selecting_multiple_items_with_a_two-finger_pan_gesture

//CollectionViewCell.swift
//=====================
/*
See LICENSE folder for this sample’s licensing information.

Abstract:
A custom collection view cell that `CollectionViewController` displays.
*/

import UIKit

class CollectionViewCell: UICollectionViewCell {
    
    static let reuseIdentifier = "reuseIdentifier"

    @IBOutlet weak var imageView: UIImageView!
    @IBOutlet weak var imageViewOverlay: UIView!
    @IBOutlet weak var imageViewSelected: UIImageView!
    @IBOutlet weak var imageViewUnselected: UIImageView!
    

    override func awakeFromNib() {
        super.awakeFromNib()
        // Turn `imageViewSelected` into a circle to make its background
        // color act as a border around the checkmark symbol.
        imageViewSelected.layer.cornerRadius = imageViewSelected.bounds.width / 2
        imageViewUnselected.layer.cornerRadius = imageViewSelected.bounds.width / 2
        
        self.imageViewOverlay.isHidden = true;
        self.imageViewSelected.isHidden = true;
        self.imageViewUnselected.isHidden = false;
        
    }
    
    func configureCell(with model: PhotoModel) {
      
        if let image = model.image {
            imageView.image = image
        }
    }
    
    override var isSelected: Bool{
        didSet{
            if isSelected {
                self.imageViewOverlay.isHidden = false;
                self.imageViewSelected.isHidden = false;
                self.imageViewUnselected.isHidden = true;
            }else{
                self.imageViewOverlay.isHidden = true;
                self.imageViewSelected.isHidden = true;
                self.imageViewUnselected.isHidden = false;
            }
        }
    }
   
}
//CollectionViewController.swift
//=====================
/*
See LICENSE folder for this sample’s licensing information.

Abstract:
A view controller showing that supports a two-finger pan gesture for selecting multiple items.
*/

import UIKit

class CollectionViewController: UIViewController {
    
    @IBOutlet weak var collectionView: UICollectionView!
    
    private let photos = PhotoModel.generatePhotosItems(count: 100)
    private let sectionInsets = UIEdgeInsets(top: 1.0, left: 1.0, bottom: 1.0, right: 1.0)
    private var isPad = false

    override func viewDidLoad() {
        super.viewDidLoad()
        isPad = view.traitCollection.userInterfaceIdiom == .pad
        collectionView.allowsSelection = true
        collectionView.allowsMultipleSelection = true
    
        if let flowLayout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
            flowLayout.minimumLineSpacing = sectionInsets.left
            flowLayout.minimumInteritemSpacing = sectionInsets.left
            flowLayout.sectionInset = sectionInsets
            flowLayout.itemSize = itemSize()
        }
        updateUserInterface()
    }

    func updateUserInterface() {
        guard let button = navigationItem.rightBarButtonItem else { return }
        button.title = isEditing ? "Done" : "Select"
    }

    func clearSelectedItems(animated: Bool) {
        collectionView.indexPathsForSelectedItems?.forEach({ (indexPath) in
            collectionView.deselectItem(at: indexPath, animated: animated)
        })
        collectionView.reloadItems(at: collectionView.indexPathsForVisibleItems)
    }
    
    func itemSize() -> CGSize {
        let itemsPerRow: CGFloat = isPad ? 10 : 3
        let paddingSpace = sectionInsets.left * (itemsPerRow + 1)
        let availableWidth = view.frame.width - paddingSpace
        let widthPerItem = availableWidth / itemsPerRow
        
        return CGSize(width: widthPerItem, height: widthPerItem)
    }
    
  
    @IBAction func toggleSelectionMode(_ sender: Any) {
        // Toggle selection state.
        //setEditing(!isEditing, animated: true)
    }
    
}

extension CollectionViewController: UICollectionViewDataSource {

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: CollectionViewCell.reuseIdentifier, for: indexPath)

        if let photoCell = cell as? CollectionViewCell {
            photoCell.configureCell(with: photos[indexPath.item])
        }
    
        return cell
    }
    
}

extension CollectionViewController: UICollectionViewDelegate {

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        // Automatically deselect items when the app isn't in edit mode.
        
    }
    
    // MARK: - Multiple selection methods.

    /// - Tag: collection-view-multi-select
    func collectionView(_ collectionView: UICollectionView, shouldBeginMultipleSelectionInteractionAt indexPath: IndexPath) -> Bool {
        // Returning `true` automatically sets `collectionView.allowsMultipleSelection`
        // to `true`. The app sets it to `false` after the user taps the Done button.
        return true
    }
    
    func collectionView(_ collectionView: UICollectionView, didBeginMultipleSelectionInteractionAt indexPath: IndexPath) {
        // Replace the Select button with Done, and put the
        // collection view into editing mode.
        print("\(#function)")
    }
    
    func collectionViewDidEndMultipleSelectionInteraction(_ collectionView: UICollectionView) {
        print("\(#function)")
    }
    
}