【Swift】スクロール時にヘッダーを非表示にする方法を解説！

import UIKit

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
    @IBOutlet weak var tableView: UITableView!
    @IBOutlet weak var headerView: UIView!
    var isHeaderHidden = false
    var previousScrollOffset: CGFloat = 0
    let items = ["Item 1", "Item 2", "Item 3", "Item 4", "Item 5", "Item 6", "Item 7", "Item 8", "Item 9", "Item 10", "Item 11", "Item 12", "Item 13", "Item 14", "Item 15", "Item 16", "Item 17", "Item 18", "Item 19", "Item 20"]

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

    private func setupTableView() {
        tableView.dataSource = self
        tableView.delegate = self
        // UITableViewのセル登録
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")
    }

    // MARK: - UITableViewDataSource
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return items.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        cell.textLabel?.text = items[indexPath.row]
        return cell
    }

    // MARK: - UITableViewDelegate
    // 必要に応じてUITableViewDelegateメソッドをここに追加

    // MARK: - スクロールイベントの処理
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let scrollDiff = scrollView.contentOffset.y - previousScrollOffset

        if scrollDiff > 0 && scrollView.contentOffset.y > 0 {
            if !isHeaderHidden {
                UIView.animate(withDuration: 0.3, animations: {
                    self.headerView.transform = CGAffineTransform(translationX: 0, y: -self.headerView.frame.height)
                    self.adjustTableViewInset(top: self.headerView.frame.height)
                })
                isHeaderHidden = true
            }
        } else if scrollDiff < 0 && scrollView.contentOffset.y < self.headerView.frame.height {
            if isHeaderHidden {
                UIView.animate(withDuration: 0.3, animations: {
                    self.headerView.transform = .identity
                    self.adjustTableViewInset(top: 0)
                })
                isHeaderHidden = false
            }
        }
        previousScrollOffset = scrollView.contentOffset.y
    }

    private func adjustTableViewInset(top: CGFloat) {
        let insets = UIEdgeInsets(top: top, left: 0, bottom: 0, right: 0)
        tableView.contentInset = insets
        tableView.scrollIndicatorInsets = insets
    }
}