How to add a subview with constraints to make the subview with the same frame as its superview?

Question

Within UIView I have a method presentView():

public func presentView() {
    
    UIApplication.sharedApplication().delegate?.window??.addSubview(self)
    
    let blurEffect = UIBlurEffect(style: .Light)
    let blurEffectView = UIVisualEffectView(effect: blurEffect)
    blurEffectView.backgroundColor = UIColor.yellowColor()
    addSubview(blurEffectView)
    
    let topConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Top, relatedBy: .Equal, toItem: self, attribute: .Bottom, multiplier: 1, constant: 0)
    let bottomConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Bottom, relatedBy: .Equal, toItem: self, attribute: .Top, multiplier: 1, constant: 0)
    let leadingConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Leading, relatedBy: .Equal, toItem: self, attribute: NSLayoutAttribute.Leading, multiplier: 1, constant: 0)
    let trailingConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Trailing, relatedBy: .Equal, toItem: self, attribute: NSLayoutAttribute.Trailing, multiplier: 1, constant: 0)
    
    self.addConstraints([topConstraint, bottomConstraint, leadingConstraint, trailingConstraint])
    
    print("newframe: \(blurEffectView.frame)")

}

but something is wrong because this is the output on console:

newframe: (0.0, 0.0, 0.0, 0.0)

and result is:

If I'm reading correctly, self is a UIView. Then you should add the constraints to self rather then blurEffectView. — Dániel Nagy
– Dániel Nagy, Commented Sep 28, 2015 at 12:11
@DánielNagy I updated the question, can you help me to solve this out? — Bartłomiej Semańczyk
– Bartłomiej Semańczyk, Commented Sep 28, 2015 at 12:35
I think until the view is not layed out, you won't get it's actual frame. So after self.addConstraints you won't get it right now. — Dániel Nagy
– Dániel Nagy, Commented Sep 28, 2015 at 13:00
Again updated the question with new info. I set background color to yellow, but there is no my view at all. — Bartłomiej Semańczyk
– Bartłomiej Semańczyk, Commented Sep 28, 2015 at 13:04
This SO question has a lot of good information on programmatically adding constraints. — Derek Soike
– Derek Soike, Commented Mar 9, 2018 at 20:39

pkamb · Accepted Answer · 2018-11-16 05:49:54Z

13

Remember about:

blurEffectView.translatesAutoresizingMaskIntoConstraints = false

and then:

let topConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Top, relatedBy: .Equal, toItem: self, attribute: .Top, multiplier: 1, constant: 0)
let bottomConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Bottom, relatedBy: .Equal, toItem: self, attribute: .Bottom, multiplier: 1, constant: 0)
let leadingConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Leading, relatedBy: .Equal, toItem: self, attribute: .Leading, multiplier: 1, constant: 0)
let trailingConstraint = NSLayoutConstraint(item: blurEffectView, attribute: .Trailing, relatedBy: .Equal, toItem: self, attribute: .Trailing, multiplier: 1, constant: 0)

addSubview(blurEffectView)
addConstraints([topConstraint, bottomConstraint, leadingConstraint, trailingConstraint])
layoutIfNeeded()

edited Nov 16, 2018 at 5:49

pkamb

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answered Sep 29, 2015 at 17:54

Bartłomiej Semańczyk

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