Constraint Crash after Dismissing View Controller - ios

Question

I'm a bit new to Xcode and been trying to do things programatically. I have View Controller A, B, C, and D. I have a back button on C, and D. When going from D to C using self.dismiss it works fine, however when I go from C to B I am getting a crash that looks like it's a constraint issue and I have no idea why.
Again, the crash occurs when going from C to B. The error says no common ancestor for DropDownButton, but there is no DropDownButton on ViewController B, it exists on C the one I am trying to dismiss.
I would like to know more about how the view controllers dismissing and Auto Layout works, could someone point me in the right direction please?
"oneonone.DropDownButton:0x7fcfe9d30660'🇺🇸+1 ⌄'.bottom"> because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That's illegal. userInfo: (null)
2018-11-09 19:56:22.828322-0600 oneonone[62728:4835265] *** Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to activate constraint with anchors <NSLayoutYAxisAnchor
UPDATE TO QUESTIONS:
Here is View Controller C, included is the var, adding it to subview, and how I dismiss this view controller
lazy var countryCodes: DropDownButton = {
let button = DropDownButton(frame: CGRect(x: 0, y: 0, width: 0, height: 0))
let us = flag(country: "US")
let br = flag(country: "BR")
let lightGray = UIColor(red: 240/255, green: 240/255, blue: 240/255, alpha: 1)
button.backgroundColor = lightGray
button.setTitle(us + "+1 \u{2304}", for: .normal)
button.titleLabel?.font = UIFont.systemFont(ofSize: 20)
button.setTitleColor(UIColor.darkGray, for: .normal)
button.uiView.dropDownOptions = [us + "+1", br + "+55", "+33", "+17", "+19"]
return button
}()
override func viewDidLoad() {
super.viewDidLoad()
self.view.backgroundColor = .white
[countryCodes].forEach{ view.addSubview($0) }
setupLayout()
}
func setupLayout(){
countryCodes.translatesAutoresizingMaskIntoConstraints = false
countryCodes.topAnchor.constraint(equalTo: instructionLabel.bottomAnchor, constant: 30).isActive = true
countryCodes.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: -77.5).isActive = true
countryCodes.widthAnchor.constraint(equalToConstant: 85).isActive = true // guarantees this width for stack
countryCodes.heightAnchor.constraint(equalToConstant: 40).isActive = true
}
#objc func buttonPressed(){
self.dismiss(animated: true, completion: nil)
}
Here is the code in view controller B that (creates or presents?) View Controller C
#objc func phoneAuthButtonPressed(){
let vc = phoneAuthViewController()
self.present(vc, animated: true, completion: nil)
}
UPDATE 2: ADDING THE CUSTOM CLASS
Here is the button code that I used as a custom class following a tutorial, I believe the problem lies in here
protocol dropDownProtocol {
func dropDownPressed(string: String)
}
class DropDownButton: UIButton, dropDownProtocol {
var uiView = DropDownView()
var height = NSLayoutConstraint()
var isOpen = false
func dropDownPressed(string: String) {
self.setTitle(string + " \u{2304}", for: .normal)
self.titleLabel?.font = UIFont.systemFont(ofSize: 18)
self.dismissDropDown()
}
override init(frame: CGRect) {
super.init(frame: frame)
self.backgroundColor = UIColor.gray
uiView = DropDownView.init(frame: CGRect.init(x: 0, y: 0, width: 0, height: 0))
uiView.delegate = self
uiView.layer.zPosition = 1 // show in front of other labels
uiView.translatesAutoresizingMaskIntoConstraints = false
}
override func didMoveToSuperview() {
self.superview?.addSubview(uiView)
self.superview?.bringSubviewToFront(uiView)
uiView.topAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
uiView.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
uiView.widthAnchor.constraint(equalTo: self.widthAnchor).isActive = true
height = uiView.heightAnchor.constraint(equalToConstant: 0)
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) { // animates drop down list
NSLayoutConstraint.deactivate([self.height])
if self.uiView.tableView.contentSize.height > 150 {
self.height.constant = 150
} else {
self.height.constant = self.uiView.tableView.contentSize.height
}
if isOpen == false {
isOpen = true
NSLayoutConstraint.activate([self.height])
UIView.animate(withDuration: 0.25, delay: 0, options: .curveEaseInOut, animations: {
self.uiView.layoutIfNeeded()
self.uiView.center.y += self.uiView.frame.height / 2
}, completion: nil)
} else {
dismissDropDown()
}
}
func dismissDropDown(){
isOpen = false
self.height.constant = 0
NSLayoutConstraint.activate([self.height])
UIView.animate(withDuration: 0.25, delay: 0, options: .curveEaseInOut, animations: {
self.uiView.center.y -= self.uiView.frame.height / 2
self.uiView.layoutIfNeeded()
}, completion: nil)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
class DropDownView: UIView, UITableViewDelegate, UITableViewDataSource {
var dropDownOptions = [String]()
var tableView = UITableView()
var delegate : dropDownProtocol!
let lightGray = UIColor(red: 240/255, green: 240/255, blue: 240/255, alpha: 1)
override init(frame: CGRect) {
super.init(frame: frame)
tableView.backgroundColor = lightGray
tableView.delegate = self
tableView.dataSource = self
tableView.translatesAutoresizingMaskIntoConstraints = false
self.addSubview(tableView) // can not come after constraints
tableView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
tableView.leadingAnchor.constraint(equalTo: self.leadingAnchor).isActive = true
tableView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
tableView.trailingAnchor.constraint(equalTo: self.trailingAnchor).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return dropDownOptions.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell()
cell.textLabel?.text = dropDownOptions[indexPath.row]
cell.textLabel?.font = UIFont.systemFont(ofSize: 14)
cell.textLabel?.textColor = UIColor.darkGray
cell.backgroundColor = lightGray
return cell
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
self.delegate.dropDownPressed(string: dropDownOptions[indexPath.row])
self.tableView.deselectRow(at: indexPath, animated: true)
}
}

Answer 1

Replace your didMoveToSuperview function with this and it will work. This function also gets called when the view its removed from the superview and the superview will be nil and that's causing the crash.
override func didMoveToSuperview() {
if let superview = self.superview {
self.superview?.addSubview(dropView)
self.superview?.bringSubviewToFront(dropView)
dropView.topAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
dropView.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
dropView.widthAnchor.constraint(equalTo: self.widthAnchor).isActive = true
height = dropView.heightAnchor.constraint(equalToConstant: 0)
}
}

Answer 2

As I can see, the error says that one of countryCodes buttons is located in the different view than instructionLabel. They should have the same parent if you want them to be constrained by each other.

Answer 3

Hi I think the problem occurs in the didMoveToSuperView() function, because it is called also when the view is removed from it's superview. so when you try to setup the anchor to something that does no more exist it crashes.
try something like this :
if let superview = self.superview {
superview.addSubview(uiView)
superview.bringSubviewToFront(uiView)
uiView.topAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
uiView.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
uiView.widthAnchor.constraint(equalTo: self.widthAnchor).isActive = true
height = uiView.heightAnchor.constraint(equalToConstant: 0)
}