UIKit Change Presented View Controller's Layout Constraints Relative to Parent View - ios

Question

I'm working on a project in UIKit, without storyboards (only programmatic layout constraints) and, following this, I have a custom view controller like this:
#objc public class testController: UIViewController, QLPreviewControllerDataSource {
public override func viewDidAppear(_ animated: Bool) {
let previewController = QLPreviewController()
previewController.dataSource = self
self.view.translatesAutoresizingMaskIntoConstraints = false
previewController.view.widthAnchor.constraint(equalToConstant: 200).isActive = true
present(previewController, animated: true, completion: nil)
}
public func numberOfPreviewItems(in controller: QLPreviewController) -> Int {
return 1
}
public func previewController(_ controller: QLPreviewController, previewItemAt index: Int) -> QLPreviewItem {
guard let url = Bundle.main.url(forResource: String("beans"), withExtension: "pdf") else {
fatalError("Could not load \(index).pdf")
}
return url as QLPreviewItem
}
}
Then, in my main View Controller file, I add this testController as a subview like so:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
let test = testController()
self.view.addSubview(test.view)
test.view.translatesAutoresizingMaskIntoConstraints = false
}
}
This works fine, but I'd like to be able to change my testController's programmatic layout constraints relative to it's parent view.
I've tried stuff like this in the main view controller (ViewController):
let test = testController()
self.view.addSubview(test.view)
test.view.translatesAutoresizingMaskIntoConstraints = false
test.view.widthAnchor.constraint(equalTo: 200, constant: 0).isActive = true
but this simply doesn't work/the view doesn't reflect these constraints at all and it seems like the only way I can successfully modify the constraints of the testController, is within the viewDidAppear function of the testController class.
However, if I try something like this:
public override func viewDidAppear(_ animated: Bool) {
let previewController = QLPreviewController()
previewController.dataSource = self
self.view.translatesAutoresizingMaskIntoConstraints = false
previewController.view.widthAnchor.constraint(equalToConstant: 200).isActive = true //notice how this works since it's a hardcoded 200
previewController.view.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: 0).isActive = true //this throws an error
present(previewController, animated: true, completion: nil)
}
I get an error thrown.
So I'd somehow like to access the parent of testViewController I guess, and use it for the constraints of the view. I've tried unsuccessfully using presentingViewController and parent for this, but they either return nil or throw an error.
Any help here would be appreciated.

Answer 1

This is sample to add view and change the constraints, in your example you have to add more constraint to test view.
class ViewController: UIViewController {
let buttonTest: UIButton = {
let button = UIButton()
button.setTitle("go to ", for: .normal)
button.backgroundColor = .green
button.addTarget(self, action: #selector(buttonPressed), for: .touchUpInside)
return button
}()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
self.view.addSubview(buttonTest)
buttonTest.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
buttonTest.centerYAnchor.constraint(equalTo: self.view.centerYAnchor),
buttonTest.centerXAnchor.constraint(equalTo: self.view.centerXAnchor)
])
}
#objc func buttonPressed() {
let secondView = SecondViewController()
self.view.addSubview(secondView.view)
secondView.view.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
secondView.view.topAnchor.constraint(equalTo: self.view.topAnchor,constant: 100),
secondView.view.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
secondView.view.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
secondView.view.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: -100)
])
}
}
class SecondViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
self.view.backgroundColor = .blue
}
}