CODEWITHSUNDEEP
iosswift
Chameleon
Chameleon

Reputation: 1608

Proper code to delete/or deactivate one constraint to add another to UIView

Why am I getting a Thread 1: signal SIGABRT?

I am trying to learn how to delete and create new constraints to UIViews

import UIKit

class ViewController: UIViewController {
@IBOutlet weak var red: UIView!
@IBOutlet weak var green: UIView!
@IBOutlet weak var redTop: NSLayoutConstraint!
@IBOutlet weak var greenToRed: NSLayoutConstraint!

@IBAction func shift(sender: AnyObject) {
    green.removeConstraint(greenToRed)
    let newGreen = NSLayoutConstraint(item: green, attribute: .Top, relatedBy: .Equal, toItem: view, attribute: .Top, multiplier: 1, constant: 0)
    green.addConstraint(newGreen)
    newGreen.active = true
    red.removeConstraint(redTop)
    let newRed = NSLayoutConstraint(item: red, attribute: .Top, relatedBy: .Equal, toItem: green, attribute: .Bottom, multiplier: 1, constant: 10)
    red.addConstraint(newRed)
    newRed.active = true}   }

constraints

Upvotes: 0

Views: 104

Answers (1)

rdelmar
rdelmar

Reputation: 104082

Constraints on a subview need to be added to the superview of the view involved. So a constraint between green and view needs to be added to view (since it's the superview of green). Similarly, a constraint between red and green also needs to be added to their common superview, view (the controllers self.view).

From Apple's documentation: "To make a constraint active, you must add it to a view. The view that holds the constraint must be an ancestor of the views the constraint involves, and should usually be the closest common ancestor. (This is in the existing NSView API sense of the word ancestor, where a view is an ancestor of itself.)".

Upvotes: 1

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