UIKit - Swift - Allow tableHeaderView to scroll up, but not down - ios

Question

I have a UIViewController with a navigation bar and a tab bar. Other than that, the whole screen is made up of a UITableView.
I have a large tableHeaderView that has the same background color as the navbar.
When I drag the content up (scrolling down) everything looks fine.
But if I drag it up, there is an ugly disconnection between the navigation bar and the header view.
Is there any way I could anchor it to the top when dragging down, while allowing it to scroll when dragging up?

Answer 1

You can try creating a view and placing it behind the tableView, as the table view scrolls, the height of the view is updated.
import UIKit
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
lazy var tableView : UITableView = {
let tableView = UITableView(frame: .zero, style: .plain)
tableView.dataSource = self
tableView.delegate = self
return tableView
}()
let backView : UIView = {
let view = UIView()
view.backgroundColor = .red
return view
}()
var backViewHeight : NSLayoutConstraint?
override func viewDidLoad() {
super.viewDidLoad()
self.title = "ViewController"
self.view.addSubview(backView)
backView.translatesAutoresizingMaskIntoConstraints = false
backView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor).isActive = true
backView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
backView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
backViewHeight = backView.heightAnchor.constraint(equalToConstant: 0)
backViewHeight?.isActive = true
self.view.addSubview(tableView)
tableView.translatesAutoresizingMaskIntoConstraints = false
tableView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor).isActive = true
tableView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
tableView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
tableView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
tableView.register(Cell.self, forCellReuseIdentifier: "cell")
tableView.register(Header.self, forHeaderFooterViewReuseIdentifier: "header")
tableView.backgroundColor = .clear
self.navigationController?.navigationBar.barTintColor = .red
self.navigationController?.navigationBar.isTranslucent = false
self.navigationController?.navigationBar.setValue(true, forKey: "hidesShadow")
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 3
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if scrollView.contentOffset.y < 0 {
backViewHeight?.constant = -scrollView.contentOffset.y
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
return cell
}
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let header = tableView.dequeueReusableHeaderFooterView(withIdentifier: "header")
header?.contentView.backgroundColor = .red
let headerLabel = UILabel(frame: CGRect(x: 0, y: 0, width: tableView.bounds.size.width, height: 100))
headerLabel.textAlignment = .center
headerLabel.text = "Header"
header?.addSubview(headerLabel)
return header
}
func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
return 100
}
func tableView(_ tableView: UITableView, viewForFooterInSection section: Int) -> UIView? {
let view = UIView()
view.backgroundColor = .white
return view
}
}
class Cell: UITableViewCell {
let label : UILabel = {
let label = UILabel()
label.text = "One Label"
return label
}()
override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
super.init(style: style, reuseIdentifier: reuseIdentifier)
self.backgroundColor = .clear
setupViews()
}
func setupViews() {
self.backgroundColor = .white
self.addSubview(label)
label.frame = self.frame
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
class Header : UITableViewHeaderFooterView {
override init(reuseIdentifier: String?) {
super.init(reuseIdentifier: reuseIdentifier)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
If you copy paste this code in an empty project you can have a look at the behavior. Don't forget to embed the ViewController in a NavigationController. Hope it helps

Answer 2

1) If an unwanted white space on the top of tableview is permanent and the constraints are correct this is the solution.
the scroll view insets adjusted automatically if you disable it should remove it
if #available(iOS 11.0, *) {
tableView.contentInsetAdjustmentBehavior = .never
} else {
automaticallyAdjustsScrollViewInsets = false
}
2) if u just have it when u pull down and it goes back to its normal state. It means is that the tableview bouncing is enabled and that is normal behaviour according to iOS documentation:
If the value of this property is true, the scroll view bounces when it encounters a boundary of the content. Bouncing visually indicates that scrolling has reached an edge of the content. If the value is false, scrolling stops immediately at the content boundary without bouncing. The default value is true.
you can uncheck the bouncing from the tableview in your storyboard or xib file. Or u can use this snippet:
tableView.bounces = false
tableView.alwaysBounceVertical = false
Note: that is not recommended to disable the scroll bouncing since it would make things feel very unnatural for iOS.
and also if you want to use pull to refresh it will not work.
So finally if u choose to not disable it you will have to change the background color of the parent of your tableview and it will solve it.
I hope that makes sense!