UIScrollView does not scroll + second scrollView shows nothing - swift

Question

it is unpleasant for me but I need some help with my UIScrollViews. They are both arranged subviews of a stackView on my MainVC.
The weird thing is that only one of them is showing content, although I used the same code for both scrollViews. The second problem is that they do not scroll, here is my code:
class HomeVC: UIViewController, UIScrollViewDelegate {
var views = [UIImageView]()
//StackView
let stackView = UIStackView()
let topView = UIScrollView()
let bottomView = UIScrollView()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = MyColors.soft_pink
prepare_data()
print(views.count)
}
//MARK: - GUI
func setUpStackView() {
view.addSubview(stackView)
stackView.alignment = .center
stackView.axis = .vertical
stackView.distribution = .equalCentering
stackView.spacing = 5
stackView.addArrangedSubview(topView)
stackView.addArrangedSubview(bottomView)
stackView.translatesAutoresizingMaskIntoConstraints = false
stackView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20).isActive = true
stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10).isActive = true
stackView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10).isActive = true
stackView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -25).isActive = true
setUpTopView()
setUpBottomView()
}
func setUpTopView() {
topView.delegate = self
topView.layer.cornerRadius = 25
topView.layer.masksToBounds = true
topView.layer.borderWidth = 10
topView.layer.borderColor = UIColor.white.cgColor
topView.contentMode = .scaleAspectFit
topView.showsHorizontalScrollIndicator = false
topView.isPagingEnabled = true
topView.contentSize = CGSize(width: topView.frame.width * CGFloat(views.count),height: topView.frame.height)
for i in 0..<views.count {
topView.addSubview(views[i])
views[i].frame = CGRect(x: topView.frame.width * CGFloat(i), y: 0, width: 350, height: 250)
views[i].layer.cornerRadius = 25
}
topView.translatesAutoresizingMaskIntoConstraints = false
topView.leadingAnchor.constraint(equalTo: stackView.leadingAnchor, constant: 10).isActive = true
topView.trailingAnchor.constraint(equalTo: stackView.trailingAnchor, constant: -10).isActive = true
topView.heightAnchor.constraint(equalToConstant: 250).isActive = true
}
func setUpBottomView() {
bottomView.delegate = self
bottomView.layer.cornerRadius = 25
bottomView.layer.masksToBounds = true
bottomView.layer.borderWidth = 10
bottomView.layer.borderColor = UIColor.white.cgColor
bottomView.contentMode = .scaleAspectFit
bottomView.showsHorizontalScrollIndicator = false
bottomView.isPagingEnabled = true
bottomView.contentSize = CGSize(width: bottomView.frame.width * CGFloat(views.count),height: bottomView.frame.height)
for i in 0..<views.count {
bottomView.addSubview(views[i])
views[i].frame = CGRect(x: bottomView.frame.width * CGFloat(i), y: 0, width: 350, height: 250)
views[i].layer.cornerRadius = 25
}
bottomView.translatesAutoresizingMaskIntoConstraints = false
bottomView.leadingAnchor.constraint(equalTo: stackView.leadingAnchor, constant: 10).isActive = true
bottomView.trailingAnchor.constraint(equalTo: stackView.trailingAnchor, constant: -10).isActive = true
bottomView.heightAnchor.constraint(equalToConstant: 250).isActive = true
}
func prepare_data() {
for x in 1...6 {
let woman = UIImage(named: "woman\(x)")
let womanView = UIImageView(image: woman)
womanView.contentMode = .scaleAspectFill
views.append(womanView)
}
setUpStackView()
}
}
Could someone please be so kind and tell me what I have wrong? Thank you in advance!

Answer 1

Try to debug by printing values. bottomView.frame.width was zero at initialisation, so update subviews in viewDidLayoutSubviews. There are more ways you can look for frame update detection.
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
DispatchQueue.main.async {
self.updateSubviewFrames()
}
}
func updateSubviewFrames() {
print(bottomView.frame)
bottomView.contentSize = CGSize(width: bottomView.frame.width * CGFloat(views.count),height: bottomView.frame.height)
for i in 0..<views.count {
views[i].frame = CGRect(x: bottomView.frame.width * CGFloat(i), y: 0, width: 350, height: 250)
views[i].layer.cornerRadius = 25
}
}

Answer 2

You've done a few things wrong...
First, because it's easy -- the reason you don't see anything in your Top scroll view is because you add your image views (from the views array) to topView, and then you add them to bottomView which removes them from topView!
So, you need one array of views for topView and an array of other views for bottomView.
Next, you are using auto-layout / constraints to size and position your stack view, then trying to use the frames of the stack view's arranged subviews -- for example:
bottomView.contentSize = CGSize(width: bottomView.frame.width * CGFloat(views.count),height: bottomView.frame.height)
but, that's all being done in functions called from viewDidLoad() when auto-layout has not yet configured the view frames.
You're also adding your scroll view's as arranged subviews of the stack view, but then constraining them to the stack view (which is not the way to do it):
topView.leadingAnchor.constraint(equalTo: stackView.leadingAnchor, constant: 10).isActive = true
As a side note: the easiest way to manage a paged scroll view is to embed the "pages" (your image views) in a horizontal stack view, setting the width of each view to the width of the scroll view's Frame Layout Guide (minus desired spacing).
Here's a modified version of your code to take a look at:
class HomeVC: UIViewController, UIScrollViewDelegate {
var topViews = [UIImageView]()
var botViews = [UIImageView]()
//StackView
let stackView = UIStackView()
let topView = UIScrollView()
let bottomView = UIScrollView()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .systemPink // MyColors.soft_pink
prepare_data()
setUpStackView()
setUpTopAndBottomViews()
}
func prepare_data() {
// create 6 image views
// for BOTH Top and Bottom scroll views
// I'll assume you have "woman" and "man" images
for x in 1...6 {
let woman = UIImage(named: "woman\(x)")
let man = UIImage(named: "man\(x)")
let womanView = UIImageView(image: woman)
womanView.contentMode = .scaleAspectFill
topViews.append(womanView)
let manView = UIImageView(image: man)
manView.contentMode = .scaleAspectFill
botViews.append(manView)
}
}
func setUpStackView() {
// setup stack view
view.addSubview(stackView)
// .alignment should be .fill, not .center
//stackView.alignment = .center
stackView.alignment = .fill
stackView.axis = .vertical
// let's use .fillEqually instead of .equalCentering
//stackView.distribution = .equalCentering
stackView.distribution = .fillEqually
stackView.spacing = 5
stackView.addArrangedSubview(topView)
stackView.addArrangedSubview(bottomView)
stackView.translatesAutoresizingMaskIntoConstraints = false
stackView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20).isActive = true
stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10).isActive = true
stackView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10).isActive = true
stackView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -25).isActive = true
}
func setUpTopAndBottomViews() {
// setup both scroll views with the same properties
[topView, bottomView].forEach { v in
v.delegate = self
v.layer.cornerRadius = 25
v.layer.masksToBounds = true
v.layer.borderWidth = 10
v.layer.borderColor = UIColor.white.cgColor
v.showsHorizontalScrollIndicator = false
v.isPagingEnabled = true
}
// let's use auto-layout here
// if you want horizontal paged scrolling, easiest route is to
// use a horizontal stack view
// create a stack view
let topStack = UIStackView()
topStack.translatesAutoresizingMaskIntoConstraints = false
topStack.spacing = 10
// add stack view to topView
topView.addSubview(topStack)
for i in 0..<topViews.count {
topStack.addArrangedSubview(topViews[i])
topViews[i].layer.cornerRadius = 25
// set view width and height equal to
// topView's Frame Layout Guide
// allowing for 5-pts "padding" on the sides
topViews[i].widthAnchor.constraint(equalTo: topView.frameLayoutGuide.widthAnchor, constant: -10.0).isActive = true
topViews[i].heightAnchor.constraint(equalTo: topView.frameLayoutGuide.heightAnchor).isActive = true
}
// now we'll set constraints on the stack view to
// topView's Content Layout Guide
NSLayoutConstraint.activate([
topStack.topAnchor.constraint(equalTo: topView.contentLayoutGuide.topAnchor),
topStack.leadingAnchor.constraint(equalTo: topView.contentLayoutGuide.leadingAnchor, constant: 5.0),
topStack.trailingAnchor.constraint(equalTo: topView.contentLayoutGuide.trailingAnchor, constant: -5.0),
topStack.bottomAnchor.constraint(equalTo: topView.contentLayoutGuide.bottomAnchor),
])
// same thing with the bottom scroll view
// create a new stack view
let botStack = UIStackView()
botStack.translatesAutoresizingMaskIntoConstraints = false
botStack.spacing = 10
// add stack view to bottomView
bottomView.addSubview(botStack)
for i in 0..<botViews.count {
botStack.addArrangedSubview(botViews[i])
botViews[i].layer.cornerRadius = 25
// set view width and height equal to
// bottomView's Frame Layout Guide
// allowing for 5-pts "padding" on the sides
botViews[i].widthAnchor.constraint(equalTo: bottomView.frameLayoutGuide.widthAnchor, constant: -10.0).isActive = true
botViews[i].heightAnchor.constraint(equalTo: bottomView.frameLayoutGuide.heightAnchor).isActive = true
}
// now we'll set constraints on the stack view to
// bottomView's Content Layout Guide
NSLayoutConstraint.activate([
botStack.topAnchor.constraint(equalTo: bottomView.contentLayoutGuide.topAnchor),
botStack.leadingAnchor.constraint(equalTo: bottomView.contentLayoutGuide.leadingAnchor, constant: 5.0),
botStack.trailingAnchor.constraint(equalTo: bottomView.contentLayoutGuide.trailingAnchor, constant: -5.0),
botStack.bottomAnchor.constraint(equalTo: bottomView.contentLayoutGuide.bottomAnchor),
])
}
}