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

Solution 1

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];

Solution 2

Here is the syntax for Swift 3:

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

Comments

[fabb]

Is this doable from interface builder too?

[fabb]

Yes it is since Xcode 6! In the Pin Tool there now is an option for Aspect.

[Evgenii]

I think it needs to swap NSLayoutAttributeHeight and NSLayoutAttributeWidth. Right now it says 3:4 and not 4:3.

[D6mi]

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.