Cannot see Buttons in UIScrollView - swift

Question

I was making a list in the form of scrollview in swift where the view consists of various types such as labels, button etc.
However when i added the button to the subview, they were not displayed although all other labels etc were displayed. I also tried messing around in the constraints and anchors.
On the other hand when i added the same button to self.view.addsubview instead of scrollview.addsubview, they were displayed just not scrolling since not a part of the scrollview anymore.
I even removed the label to make sure that the buttons were not being overlapped(didn't work either)
I also tried to see the code in "code debug hierarchy " (3D mode), i couldn't see the button there either even though i had added it
Below is my code with an example of label, scrollview and button. It be great if anyone could provide any insights.....thanks either way....
................scrollview..........................
var editInfoView : UIScrollView = {
let view = UIScrollView()
view.translatesAutoresizingMaskIntoConstraints = false
view.contentSize.height = 700
view.backgroundColor = tableBackGroundColor
view.frame = CGRect(x: 0, y: 220, width: 375, height: 400)
return view
}()
.......................label...................
vehicleNumberLabel.translatesAutoresizingMaskIntoConstraints = false
vehicleNumberLabel.textColor = .white
vehicleNumberLabel.text = "Vehicle Number"
vehicleNumberLabel.textAlignment = .left
editInfoView.addSubview(vehicleNumberLabel)
vehicleNumberLabel.leftAnchor.constraint(equalTo: editInfoView.leftAnchor).isActive = true
vehicleNumberLabel.topAnchor.constraint(equalTo: editInfoView.topAnchor, constant: 100).isActive = true
vehicleNumberLabel.widthAnchor.constraint(equalToConstant: 160).isActive = true
vehicleNumberLabel.heightAnchor.constraint(equalToConstant: 20).isActive = true
.....................button................................
vehicleNumberButton.translatesAutoresizingMaskIntoConstraints = false
vehicleNumberButton.setTitleColor(tableTextColor, for: .normal)
vehicleNumberButton.setTitle("Vehicle Number", for: .normal)
vehicleNumberButton.tintColor = tableTextColor
vehicleNumberButton.backgroundColor = tableTextColor
editInfoView.addSubview(vehicleNumberButton)
vehicleNumberButton.rightAnchor.constraint(equalTo: editInfoView.rightAnchor).isActive = true
vehicleNumberButton.topAnchor.constraint(equalTo: editInfoView.topAnchor, constant: 400).isActive = true
vehicleNumberButton.widthAnchor.constraint(equalToConstant: 600).isActive = true
vehicleNumberButton.heightAnchor.constraint(equalToConstant: 255).isActive = true

Answer 1

Although I cannot determine the root cause of your issue with the code and explanation provided I suspect the frame of your UIScrollView() is zero after viewDidAppear(_:) adding subviews to a CGRect.zero can cause some strange behavior with the layout engine. When we create constraints programmatically we are creating a combination of inequalities, equalities, and priorities to restrict the view to a particular frame. If a the value of these constraint equations is incorrect it changes how your relating views appear. Its good practice to avoid the use of leftAnchor and rightAnchor as well, because views may flip direction based on language (writing direction) and user settings.
ViewController.swift
import UIKit
class ViewController: UIViewController {
var editInfoScrollView : UIScrollView = {
let view = UIScrollView()
view.translatesAutoresizingMaskIntoConstraints = false
view.isUserInteractionEnabled = true
view.alwaysBounceVertical = true
view.isScrollEnabled = true
view.contentSize.height = 700
view.backgroundColor = UIColor.red.withAlphaComponent(0.3)
// Does nothing because `translatesAutoresizingMaskIntoConstraints = false`
// Instead, set the content size after activating constraints in viewDidAppear
//view.frame = CGRect(x: 0, y: 220, width: 375, height: 400)
return view
}()
var vehicleNumberLabel: UILabel = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
label.textColor = UIColor.black
label.text = "Vehicle Number"
label.textAlignment = .left
return label
}()
lazy var vehicleNumberButton: UIButton = {
let button = UIButton()
button.translatesAutoresizingMaskIntoConstraints = false
button.tag = 1
button.setTitleColor(UIColor.black, for: .normal)
button.setTitle("Go to Vehicle", for: .normal)
button.tintColor = UIColor.white
button.backgroundColor = UIColor.clear
button.layer.cornerRadius = 30 // about half of button.frame.height
button.layer.borderColor = UIColor.black.cgColor
button.layer.borderWidth = 2.0
button.layer.masksToBounds = true
button.addTarget(self, action: #selector(handelButtons(_:)), for: .touchUpInside)
return button
}()
override func viewDidLoad() {
super.viewDidLoad()
self.view.backgroundColor = UIColor.white
self.setupSubviews()
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
self.editInfoScrollView.contentSize = CGSize(width: self.view.frame.width, height: 700.0)
}
func setupSubviews() {
self.view.addSubview(editInfoScrollView)
editInfoScrollView.addSubview(vehicleNumberLabel)
editInfoScrollView.addSubview(vehicleNumberButton)
let spacing: CGFloat = 12.0
let constraints:[NSLayoutConstraint] = [
editInfoScrollView.widthAnchor.constraint(equalTo: self.view.widthAnchor),
editInfoScrollView.heightAnchor.constraint(equalToConstant: 400.0),
editInfoScrollView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
editInfoScrollView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: 220.0),
vehicleNumberLabel.leadingAnchor.constraint(equalTo: editInfoScrollView.leadingAnchor, constant: spacing),
vehicleNumberLabel.trailingAnchor.constraint(equalTo: editInfoScrollView.trailingAnchor, constant: -spacing),
vehicleNumberLabel.centerXAnchor.constraint(equalTo: editInfoScrollView.centerXAnchor, constant: -50),
vehicleNumberLabel.heightAnchor.constraint(equalToConstant: 75.0),
vehicleNumberButton.widthAnchor.constraint(equalTo: editInfoScrollView.widthAnchor, multiplier: 0.66),
vehicleNumberButton.heightAnchor.constraint(equalToConstant: 65.0),
vehicleNumberButton.topAnchor.constraint(equalTo: vehicleNumberLabel.bottomAnchor, constant: spacing),
vehicleNumberButton.centerXAnchor.constraint(equalTo: editInfoScrollView.centerXAnchor),
]
NSLayoutConstraint.activate(constraints)
}
#objc func handelButtons(_ sender: UIButton) {
switch sender.tag {
case 0:
print("Default button tag")
case 1:
print("vehicleNumberButton was tapped")
default:
print("Nothing here yet")
}
}
}