Swift: How to fill a ScrollView from Interface Builder with UIViews programmatically - ios

Question

I am working on a project where I want the user to be able to select two methods of input for the same form. I came up with a scrollview that contains two custom UIViews (made programmatically). Here is the code for the responsible view controller:
import UIKit
class MainVC: UIViewController, UIScrollViewDelegate {
#IBOutlet weak var scrollView: UIScrollView!
#IBOutlet weak var pageControl: UIPageControl!
var customView1: CustomView1 = CustomView1()
var customView2: customView2 = CustomView2()
var frame = CGRect.zero
func setupScrollView() {
pageControl.numberOfPages = 2
frame.origin.x = 0
frame.size = scrollView.frame.size
customView1 = customView1(frame: frame)
self.scrollView.addSubview(customView1)
frame.origin.x = scrollView.frame.size.width
frame.size = scrollView.frame.size
customView2 = CustomView2(frame: frame)
self.scrollView.addSubview(customView2)
self.scrollView.contentSize = CGSize(width: scrollView.frame.size.width * 2, height: scrollView.frame.size.height)
self.scrollView.delegate = self
}
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
let pageNumber = scrollView.contentOffset.x / scrollView.frame.size.width
pageControl.currentPage = Int(pageNumber)
}
override func viewDidLoad() {
super.viewDidLoad()
setupScrollView()
scrollView.delegate = self
}
While it works, Xcode gives me an error message for auto layout:
Scrollable content size is ambiguous for "ScrollView"
Also a problem: content on the second UIView is not centered, even though it should be:
picture of the not centered content
import UIKit
class customView2: UIView {
lazy var datePicker: UIDatePicker = {
let datePicker = UIDatePicker()
datePicker.translatesAutoresizingMaskIntoConstraints = false
return datePicker
}()
//initWithFrame to init view from code
override init(frame: CGRect) {
super.init(frame: frame)
setupView()
}
//initWithCode to init view from xib or storyboard
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setupView()
}
func setupView () {
self.backgroundColor = .systemYellow
datePicker.datePickerMode = .date
datePicker.addTarget(self, action: #selector(self.datePickerValueChanged(_:)), for: .valueChanged)
addSubview(datePicker)
setupLayout()
}
func setupLayout() {
let view = self
NSLayoutConstraint.activate([
datePicker.centerXAnchor.constraint(equalTo: view.centerXAnchor),
datePicker.topAnchor.constraint(equalTo: view.topAnchor, constant: 20),
datePicker.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.5),
datePicker.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.2)
])
}
#objc func datePickerValueChanged(_ sender: UIDatePicker) {
let dateFormatter: DateFormatter = DateFormatter()
dateFormatter.dateFormat = "dd.MM.yyyy"
let selectedDate: String = dateFormatter.string(from: sender.date)
print("Selected value \(selectedDate)")
}
Any ideas on how to solve this? Thank you very much in advance. And please go easy on me, this is my first question on stackoverflow. I am also fairly new to programming in swift.

Answer 1

To make things easier on yourself,
add a horizontal UIStackView to the scroll view
set .distribution = .fillEqually
constrain all 4 sides to the scroll view's .contentLayoutGuide
constrain its height to the scroll view's .frameLayoutGuide
add your custom views to the stack view
constrain the width of the first custom view to the width of the scroll view's .frameLayoutGuide
Here is your code, modified with that approach:
class MainVC: UIViewController, UIScrollViewDelegate {
#IBOutlet weak var scrollView: UIScrollView!
#IBOutlet weak var pageControl: UIPageControl!
var customView1: CustomView1 = CustomView1()
var customView2: CustomView2 = CustomView2()
func setupScrollView() {
pageControl.numberOfPages = 2
// let's put the two custom views in a horizontal stack view
let stack = UIStackView()
stack.axis = .horizontal
stack.distribution = .fillEqually
stack.translatesAutoresizingMaskIntoConstraints = false
stack.addArrangedSubview(customView1)
stack.addArrangedSubview(customView2)
// add the stack view to the scroll view
scrollView.addSubview(stack)
let contentG = scrollView.contentLayoutGuide
let frameG = scrollView.frameLayoutGuide
NSLayoutConstraint.activate([
// constrain stack view to all 4 sides of content layout guide
stack.topAnchor.constraint(equalTo: contentG.topAnchor),
stack.leadingAnchor.constraint(equalTo: contentG.leadingAnchor),
stack.trailingAnchor.constraint(equalTo: contentG.trailingAnchor),
stack.bottomAnchor.constraint(equalTo: contentG.bottomAnchor),
// stack view Height equal to scroll view frame layout guide height
stack.heightAnchor.constraint(equalTo: frameG.heightAnchor),
// stack is set to fillEqually, so we only need to set
// width of first custom view equal to scroll view frame layout guide width
customView1.widthAnchor.constraint(equalTo: frameG.widthAnchor),
])
self.scrollView.delegate = self
}
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
let pageNumber = scrollView.contentOffset.x / scrollView.frame.size.width
pageControl.currentPage = Int(pageNumber)
}
override func viewDidLoad() {
super.viewDidLoad()
setupScrollView()
scrollView.delegate = self
}
}
Edit
Couple additional notes...
UIScrollView layout ambiguity.
As I said in my initial comment, if we add a UIScrollView in Storyboard / Interface Builder, but do NOT give it any constrained content, IB will complain that it has Scrollable Content Size Ambiguity -- because it does. We haven't told IB what the content will be.
We can either ignore it, or select the scroll view and, at the bottom of the Size Inspector pane, change Ambiguity to Never Verify.
As a general rule, you should correct all auto-layout warnings / errors, but in specific cases such as this - where we know that it's setup how we want, and we'll be satisfying constraints at run-time - it doesn't hurt to leave it alone.
UIDatePicker not being centered horizontally.
It actually is centered. If you add this line:
datePicker.backgroundColor = .green
You'll see that the object frame itself is centered, but the UI elements inside the frame are left-aligned:
From quick research, it doesn't appear that can be changed.
Now, from Apple's docs, we see:
You should integrate date pickers in your layout using Auto Layout. Although date pickers can be resized, they should be used at their intrinsic content size.
Curiously, if we add a UIDatePicker in Storyboard, change its Preferred Style to Compact, and give it centerX and centerY constraints... Storyboard doesn't believe it has an intrinsic content size.
If we add it via code, giving it only X/Y position constraints, it will show up where we want it at its intrinsic content size. But... if we jump into Debug View Hierarchy, Xcode tells us its Position and size are ambiguous.
Now, what's even more fun...
Tap that control and watch the Debug console fill with 535 Lines of auto-layout errors / warnings!!!
Some quick investigation -- these are all internal auto-layout issues, and have nothing to do with our code or layout.
We see similar issues with the iOS built-in keyboard when it starts showing auto-complete options.
Those are safe to ignore.