var constraints not appearing when assigned to a function that creates a view - swift

Question

I want my swift code to use var constraints to let the objects added to the code. I have added a gif below of what I am looking for. Right now the code below compiles but the black view you can see in the gif below is not appearing in the code below. In my code below the black box is not appearing at all.
import UIKit
public class ViewController : UIViewController {
var slider = UISlider()
var image1Width2: NSLayoutConstraint!
var iHieght: NSLayoutConstraint!
public override func viewDidLoad() {
super.viewDidLoad()
slider.value = 0.5
slider.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(slider)
slider.isUserInteractionEnabled = true
slider.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
slider.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
slider.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier: 0.1).isActive = true
slider.widthAnchor.constraint(equalTo: view.widthAnchor,multiplier: 1).isActive = true
button.frame = .init(x: self.view.bounds.midX,
y: 0,
width: 100,
height: 100)
self.view.addSubview(button)
image1Width2 = view.widthAnchor.constraint(equalTo: view.widthAnchor ,multiplier: 0.06)
iHieght = view.widthAnchor.constraint(equalTo: view.heightAnchor ,multiplier: 0.06)
slider.addTarget(self, action: #selector(increase), for: .allEvents)
}
private lazy var button: UIButton = {
let button = UIButton()
button.backgroundColor = .blue
button.setTitleColor(.white, for: .normal)
button.setTitle("add", for: .normal)
button.addTarget(self,
action: #selector(addBlackView),
for: .touchUpInside)
return button
}()
private func getBlackView() -> UIView {
let view = UIView()
view.backgroundColor = .black
image1Width2 = view.widthAnchor.constraint(equalTo: view.widthAnchor ,multiplier: 0.06)
iHieght = view.widthAnchor.constraint(equalTo: view.heightAnchor ,multiplier: 0.06)
let recognizer = UIPanGestureRecognizer(target: self, action: #selector(moveView(_:)))
view.addGestureRecognizer(recognizer)
return view
}
#objc
private func addBlackView() {
let view = getBlackView()
self.view.addSubview(view)
}
#objc
private func moveView(_ recognizer: UIPanGestureRecognizer) {
switch recognizer.state {
case .began:
print("gesture began")
case .changed:
let translation = recognizer.translation(in: self.view)
recognizer.view!.center = .init(x: recognizer.view!.center.x + translation.x,
y: recognizer.view!.center.y + translation.y)
recognizer.setTranslation(.zero, in: self.view)
default:
break
}
}
#objc func increase() {
image1Width2.constant = CGFloat(slider.value) * view.frame.size.width * 0.10
iHieght.constant = CGFloat(slider.value) * view.frame.size.width * 0.10
}
}

Answer 1

You are doing couple of mistakes when writing this code.Mainly iOS basic principles
Please refer this modified code, modify it and get your result.
class sampleViewController: UIViewController {
var image1Width2: NSLayoutConstraint!
var iHieght: NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
view.addSubview(slider)
slider.translatesAutoresizingMaskIntoConstraints = false
slider.value = 0.5
slider.isUserInteractionEnabled = true
NSLayoutConstraint.activate([
slider.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
slider.leadingAnchor.constraint(equalTo: view.leadingAnchor),
slider.heightAnchor.constraint(equalToConstant: 100),
slider.widthAnchor.constraint(equalTo: view.widthAnchor,multiplier: 1),
])
view.addSubview(button)
button.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
button.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16),
button.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 16),
button.widthAnchor.constraint(equalToConstant: 100),
button.heightAnchor.constraint(equalToConstant: 80),
])
button.addTarget(self,action: #selector(addBlackView),for: .touchUpInside)
slider.addTarget(self, action: #selector(increase), for: .allEvents)
}
let slider:UISlider = {
let slider = UISlider(frame: .zero)
return slider
}()
private lazy var button: UIButton = {
let button = UIButton()
button.backgroundColor = .blue
button.setTitleColor(.white, for: .normal)
button.setTitle("add", for: .normal)
return button
}()
let blackView: UIView = {
let view = UIView()
view.backgroundColor = .black
return view
}()
#objc
private func addBlackView() {
self.view.addSubview(blackView)
blackView.translatesAutoresizingMaskIntoConstraints = false
blackView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
blackView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
image1Width2 = blackView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.1)
image1Width2.isActive = true
iHieght = blackView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.1)
iHieght.isActive = true
view.layoutIfNeeded()
let recognizer = UIPanGestureRecognizer(target: self, action: #selector(moveView(_:)))
blackView.addGestureRecognizer(recognizer)
}
#objc private func moveView(_ recognizer: UIPanGestureRecognizer) {
switch recognizer.state {
case .began:
print("gesture began")
case .changed:
let translation = recognizer.translation(in: self.view)
recognizer.view!.center = .init(x: recognizer.view!.center.x + translation.x,
y: recognizer.view!.center.y + translation.y)
recognizer.setTranslation(.zero, in: self.view)
default:
break
}
}
#objc func increase() {
image1Width2.constant = CGFloat(slider.value) * view.frame.size.width * 0.10
iHieght.constant = CGFloat(slider.value) * view.frame.size.width * 0.10
}}