Working with Collection Views

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var collectionView: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()
        setupCollectionView()
    }

    func setupCollectionView() {
        let layout = UICollectionViewFlowLayout()
        layout.itemSize = CGSize(width: 100, height: 100)
        collectionView.collectionViewLayout = layout
        collectionView.dataSource = self
        collectionView.delegate = self
    }
}

extension ViewController: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
        return cell
    }
}

extension ViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print("Selected item at index path: \(indexPath)")
    }
}

class MyDataSource: NSObject, UICollectionViewDataSource {
    let items = ["Item 1", "Item 2", "Item 3"]
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return items.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
        cell.textLabel?.text = items[indexPath.item]
        return cell
    }
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    let item = items[indexPath.item]
    print("Selected item: \(item)")
}

func collectionView(_ collectionView: UICollectionView, shouldHighlightItemAt indexPath: IndexPath) -> Bool {
    return indexPath.item != 0 // Prevent highlighting first item
}

import UIKit

class CustomCollectionViewLayout: UICollectionViewFlowLayout {
    override func prepare() {
        super.prepare()
        itemSize = CGSize(width: 100, height: 100)
        minimumInteritemSpacing = 10
        minimumLineSpacing = 10
    }
    
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}

let flowLayout = UICollectionViewFlowLayout()
flowLayout.itemSize = CGSize(width: 100, height: 100)
flowLayout.minimumLineSpacing = 10
flowLayout.minimumInteritemSpacing = 5
flowLayout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
flowLayout.scrollDirection = .vertical

let layout = UICollectionViewFlowLayout()
layout.itemSize = CGSize(width: 100, height: 100)
layout.minimumLineSpacing = 10
layout.minimumInteritemSpacing = 5
layout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
collectionView.collectionViewLayout = layout

let layout = UICollectionViewFlowLayout()
layout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
layout.minimumLineSpacing = 5
layout.minimumInteritemSpacing = 5

let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)

class HeaderView: UICollectionReusableView {
    let label = UILabel()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupView()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setupView()
    }
    
    private func setupView() {
        label.text = "Section Header"
        label.translatesAutoresizingMaskIntoConstraints = false
        addSubview(label)
        NSLayoutConstraint.activate([
            label.centerXAnchor.constraint(equalTo: centerXAnchor),
            label.centerYAnchor.constraint(equalTo: centerYAnchor)
        ])
    }
}

// Register the header view
collectionView.register(HeaderView.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: "HeaderView")

// Dequeue the header view in your data source
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, withReuseIdentifier: String, at indexPath: IndexPath) -> UICollectionReusableView {
    let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "HeaderView", for: indexPath) as! HeaderView
    return header
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    print("Selected item at path: \(indexPath)")
}

func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
    print("Deselected item at path: \(indexPath)")
}

let layout = UICollectionViewCompositionalLayout { (sectionIndex, layoutEnvironment) -> NSCollectionLayoutSection? in
    let itemSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .absolute(50)
    )
    let item = NSCollectionLayoutItem(layoutSize: itemSize)
    
    let groupSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .absolute(50)
    )
    let group = NSCollectionLayoutGroup.horizontal(
        layoutSize: groupSize,
        subitems: [item]
    )
    
    let section = NSCollectionLayoutSection(group: group)
    section.contentInsets = .init(top: 10, leading: 10, bottom: 10, trailing: 10)
    return section
}

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var collectionView: UICollectionView!
    
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupDataSource()
    }
    
    private func setupDataSource() {
        dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { (collectionView, indexPath, item) -> UICollectionViewCell? in
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
            // Configure cell with item
            return cell
        }
    }
    
    private func updateUI() {
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections([.main])
        snapshot.appendItems([Item(title: "First Item")], toSection: .main)
        dataSource.apply(snapshot, animatingDifferences: true)
    }
}