How to update constraints dynamically? - ios

Question

I have three UIButton, I have created programmatically constraints, at some condition i am removing one of UIButton as button.removeFromSuperview() & rest of two button will set constraints as per priorities.
Issue is when i am removing one UIButton(buttonWink) then as of viewLifeCycle viewWillLayoutSubviews will called & App crashes in below line
buttonWink.translatesAutoresizingMaskIntoConstraints = false
Ofcourse because buttonWink is removed from superview however we can check before setting constraints as
if buttonWink != nil {
buttonWink.translatesAutoresizingMaskIntoConstraints = false
}
But by checking nil for every button will make code lengthy, is there any way of doing the same? i will really appreciate friends.
Output -
Here i am attaching my tried full code.
import UIKit
class MasterViewController: UIViewController {
#IBOutlet weak var buttonMessage : UIButton!
#IBOutlet weak var buttonLike : UIButton!
#IBOutlet weak var buttonWink : UIButton!
#IBAction func tapsOnLike(_ sender: UIButton) {
sender.removeFromSuperview()
}
#IBAction func tapsOnWink(_ sender: UIButton) {
sender.removeFromSuperview()
}
#IBAction func tapsOnNextButton(){
let vc = DetailViewController(nibName: "DetailViewController", bundle: nil)
navigationController?.pushViewController(vc, animated: true)
}
override func viewDidLoad() {
super.viewDidLoad()
setConstraints()
navigationController?.isNavigationBarHidden = true
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
// setConstraints()
}
override func viewWillLayoutSubviews() {
super.viewWillLayoutSubviews()
//setConstraints()
}
func setConstraints() {
if buttonMessage != nil {
buttonMessage?.translatesAutoresizingMaskIntoConstraints = false
}
buttonLike?.translatesAutoresizingMaskIntoConstraints = false
buttonWink?.translatesAutoresizingMaskIntoConstraints = false
//Constraints for Message button
let leading = NSLayoutConstraint(item: buttonMessage, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1.0, constant: 8)
leading.isActive = true
let trailingToSuperView = NSLayoutConstraint(item: buttonMessage, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: -8)
trailingToSuperView.priority = 998
trailingToSuperView.isActive = true
let bottomToSuperView = NSLayoutConstraint(item: buttonMessage, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: -8)
bottomToSuperView.isActive = true
let trailingToWink = NSLayoutConstraint(item: buttonMessage, attribute: .trailing, relatedBy: .equal, toItem: buttonWink, attribute: .leading, multiplier: 1, constant: -8)
trailingToWink.priority = 999
trailingToWink.isActive = true
let leadingToLike = NSLayoutConstraint(item: buttonMessage, attribute: .trailing, relatedBy: .equal, toItem: buttonLike, attribute: .leading, multiplier: 1.0, constant: -8)
leadingToLike.isActive = true
let alignBottomToWink = NSLayoutConstraint(item: buttonMessage, attribute: .bottom, relatedBy: .equal, toItem: buttonWink, attribute: .bottom, multiplier: 1, constant: 0)
alignBottomToWink.isActive = true
let alignBottomToLike = NSLayoutConstraint(item: buttonMessage, attribute: .bottom, relatedBy: .equal, toItem: buttonLike, attribute: .bottom, multiplier: 1, constant: 0)
alignBottomToLike.isActive = true
let equalWidthToWink = NSLayoutConstraint(item: buttonMessage, attribute: .width, relatedBy: .equal, toItem: buttonWink, attribute: .width, multiplier: 1, constant: 0)
equalWidthToWink.isActive = true
let equalWidthToLike = NSLayoutConstraint(item: buttonMessage, attribute: .width, relatedBy: .equal, toItem: buttonLike, attribute: .width, multiplier: 1, constant: 0)
equalWidthToLike.isActive = true
//Constraints for like button
let trailingLikeToSuperView = NSLayoutConstraint(item: buttonLike, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: -8)
trailingLikeToSuperView.priority = 999
trailingLikeToSuperView.isActive = true
let leadingToWink = NSLayoutConstraint(item: buttonLike, attribute: .trailing, relatedBy: .equal, toItem: buttonWink, attribute: .leading, multiplier: 1.0, constant: -8)
leadingToWink.isActive = true
//Constraints for Wink button
let trailingWinkToSuperView = NSLayoutConstraint(item: buttonWink, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: -8)
trailingWinkToSuperView.isActive = true
}
}

Answer 1

Just FYI -
simply use a stack view for this.
It is incredibly easy: it's why Apple finally added a stack concept a couple yrs ago.

Answer 2

I just added UIStackView & it's too easy,
Three buttons are added in horizontal stack view with 8 points spacing & added three constraints to stack view as leading, trailing & bottom to superview
#IBOutlet weak var stackView: UIStackView!
#IBAction func tapsOnLikeInStack(_ sender: UIButton) {
sender.isHidden = true
}
#IBAction func tapsOnWinkInStack(_ sender: UIButton) {
sender.isHidden = true
}
func constraintsForStackView(){
stackView?.translatesAutoresizingMaskIntoConstraints = false
stackView.spacing = 8
stackView.axis = .horizontal
stackView.distribution = .fillEqually
stackView.alignment = .fill
let leading = NSLayoutConstraint(item: stackView, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1.0, constant: 8)
leading.isActive = true
let trailingToSuperView = NSLayoutConstraint(item: stackView, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: -8)
trailingToSuperView.isActive = true
let bottomToSuperView = NSLayoutConstraint(item: stackView, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: -120)
bottomToSuperView.isActive = true
}

Answer 3

as far as your viewWillLayoutSubviews code put your buttons into an array to use:
for btn in buttons {
if (btn.superview != nil) {
btn.translatesAutoresizingMaskIntoConstraints = false
}
}
and if you want to change the constraints for the buttons still in the view, give them identifiers when you create the constraints:
for btn in buttons {
if btn.superview != nil {
btn.translatesAutoresizingMaskIntoConstraints = false
for constraint in btn.constraints {
switch constraint.identifier {
case "winkBtnTrailing":
//do stuff like constraint = new layout constraint
//or constraint.firstItem = *new first Item to base trailing on*
break
default:
//don't do stuff?
break
}
}
}
}
Just as a FYI using button.removeFromSuperview() doesn't set that button to nil, it just removes it from the view you called .addSubview(button) on