Custom Aspect Ratio with AutoLayout

Question

Let's say I have a UIView that contains a child UIView which has to be 4:3. I want to solve this problem using AutoLayout in code.

I've been struggling with AutoLayout but I haven't figured out yet how to do this.

Do you know how to solve this problem?

Thank you very much.

I attach an image to explain better what I mean. http://d.pr/i/d0Oc

score 96 · Accepted Answer · edited Aug 21 '15 at 06:47

96

I figured out.

//Given a childView... 
NSLayoutConstraint *constraint =[NSLayoutConstraint
                           constraintWithItem:childView
                           attribute:NSLayoutAttributeWidth
                           relatedBy:NSLayoutRelationEqual
                           toItem:childView
                           attribute:NSLayoutAttributeHeight
                           multiplier:4.0/3.0 //Aspect ratio: 4*height = 3*width
                           constant:0.0f];
            [childView addConstraint:constraint];

edited Aug 21 '15 at 06:47

dlinsin

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answered Sep 21 '12 at 08:11

JaviAlgaba

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Is this doable from interface builder too? – fabb Sep 18 '14 at 09:20
1

Yes it is since Xcode 6! In the Pin Tool there now is an option for Aspect. – fabb Sep 18 '14 at 09:35
3

I think it needs to swap NSLayoutAttributeHeight and NSLayoutAttributeWidth. Right now it says 3:4 and not 4:3. – Evgenii Nov 18 '14 at 06:08
2

Also, a good thing to add here, is that you cannot change the multiplier of constraints once they're created - the multiplier property's read-only. One's not able to change the multiplier even by using key paths. The way to proceed is to remove the constraint at hand and recreate it with the new multiplier. – D6mi Jan 18 '16 at 11:30

score 1 · Answer 2 · edited Dec 15 '17 at 08:11

1

Here is the syntax for Swift 3:

NSLayoutConstraint(
  item: item,
  attribute: .width,
  relatedBy: .equal,
  toItem: item,
  attribute: .height,
  multiplier: width / height,
  constant: 0)

edited Dec 15 '17 at 08:11

Bart van Kuik

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answered Mar 19 '17 at 16:02

user1615898

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tuandapen · Answer 3 · 2017-09-25T09:12:30.797

I have try all answers above but didn't work, and this is my solution with swift 3:

let newConstraint = NSLayoutConstraint(item: yourView, attribute: .width, relatedBy: .equal, toItem: yourView, attribute: .height, multiplier: 560.0/315.0, constant: 0)
yourView.addConstraint(newConstraint)
NSLayoutConstraint.activate([newConstraint])  
NSLayoutConstraint.deactivate(yourView.constraints)
yourView.layoutIfNeeded()

Custom Aspect Ratio with AutoLayout

3 Answers3

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