我很确定你实际上不可能让同一个实际细胞像那样粘在一起。不过,您可以通过自动布局技巧来创造粘性的错觉。基本上,我的建议是,您可以拥有与您想要“粘性”的单元格相同的视图,并将它们限制在粘性单元格的顶部,同时您的粘性单元格可见。如果你慢慢滚动,我能做到的最好的事情看起来并不那么完美。 (粘性单元格在捕捉到顶部或底部位置之前大部分会离开屏幕。我认为在相当正常的滚动速度下这并不明显。您的里程可能会有所不同。)
关键是设置一个表视图委托,以便您可以收到有关单元格何时出现或不出现在屏幕上的通知。
我已经包含了一个示例视图控制器。我确信我的示例代码在某些区域无法工作。 (例如,我没有处理堆叠多个“粘性”单元格或动态行高。此外,我将粘性单元格设置为蓝色,这样更容易看到粘性。)
为了运行示例代码,您应该能够将其粘贴到 Xcode 在创建新的 UIKit 应用程序时生成的默认项目中。只需用这个替换他们给你的视图控制器即可看到它的实际效果。
import UIKit
struct StickyView {
let view: UIView
let constraint: NSLayoutConstraint
}
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
lazy var stickyViewConstraints = [Int: StickyView]()
lazy var tableView: UITableView = {
let table = UITableView()
table.translatesAutoresizingMaskIntoConstraints = false
table.register(UITableViewCell.self, forCellReuseIdentifier: "cell")
table.rowHeight = 40
table.dataSource = self
table.delegate = self
return table
}()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
addTable()
setupStickyViews()
}
private func addTable() {
view.addSubview(tableView)
tableView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
tableView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
tableView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
}
private func setupStickyViews() {
let cell25 = UITableViewCell()
cell25.translatesAutoresizingMaskIntoConstraints = false
cell25.backgroundColor = .blue
cell25.textLabel?.text = "25"
view.addSubview(cell25)
cell25.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
cell25.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
cell25.heightAnchor.constraint(equalToConstant: tableView.rowHeight).isActive = true
let bottom = cell25.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor)
bottom.isActive = true
stickyViewConstraints[25] = StickyView(view: cell25, constraint: bottom)
}
// MARK: - Data Source
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return section == 0 ? 50 : 0
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = "\(indexPath.row)"
return cell
}
// MARK: - Delegate
func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
guard let stickyView = stickyViewConstraints[indexPath.row] else { return }
stickyView.constraint.isActive = false
var verticalConstraint: NSLayoutConstraint
if shouldPlaceStickyViewAtTop(stickyRow: indexPath.row) {
verticalConstraint = stickyView.view.topAnchor.constraint(equalTo: view.topAnchor)
} else {
verticalConstraint = stickyView.view.bottomAnchor.constraint(equalTo: view.bottomAnchor)
}
verticalConstraint.isActive = true
stickyViewConstraints[indexPath.row] = StickyView(view: stickyView.view, constraint: verticalConstraint)
}
private func shouldPlaceStickyViewAtTop(stickyRow: Int) -> Bool {
let visibleRows = tableView.indexPathsForVisibleRows?.map(\.row)
guard let min = visibleRows?.min() else { return false }
return min > stickyRow
}
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
if let stickyView = stickyViewConstraints[indexPath.row] {
stickyView.constraint.isActive = false
let bottom = stickyView.view.bottomAnchor.constraint(equalTo: cell.bottomAnchor)
bottom.isActive = true
stickyViewConstraints[indexPath.row] = StickyView(view: stickyView.view, constraint: bottom)
}
}
}