Set UIImageView AspectRatio constraint programmatically in swift 3

Question

I have an UIImageView in storyboard which AspectRatio is 1:1, that I want to change to 2:1 programmatically in ViewController in some cases. I create reference of that constraint in ViewController but unable to set the constraint.

Answer 1

As it's stated in Apple's guide, there're three ways to set constraints programmatically:

• You can use layout anchors
• You can use the NSLayoutConstraint class
• You can use the Visual Format Language

The most convenient and fluent way to set constraints is using Layout Anchors.

It's just one line of code to change aspect ratio for your ImageView

imageView.heightAnchor.constraint(equalTo: imageView.widthAnchor, multiplier: 1.0/2.0).isActive = true

To avoid "[LayoutConstraints] Unable to simultaneously satisfy constraints." you should add reference to your ImageView's height constraint then deactivate it:

heightConstraint.isActive = false