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Changing Constraints

After laying out a view once, how do I change some constraints ?

Simple Changes

// Initial layout
image.height(100)

// And later on
image.heightConstraint?.constant = 200

Those getters are available for left, right, top, bottom, height and width constraints

Complex changes

When we want to change the whole layout at once then the best strategy is to flush & relayout.

// Initial layout
layout(
    100,
    |-email-|,
    8,
    |-password-|,
)

// Creating an extension for getting user added constraints
extension UIView {
    var userAddedConstraints: [NSLayoutConstraint] {
        return constraints.filter { c in
            guard let cId = c.identifier else { return true }
            return !cId.contains("UIView-Encapsulated-Layout")
        }
    }
}

// remove userAddedConstraints
removeConstraints(userAddedConstraints)

// Re-apply different layout
layout(
     |-password-|,
     8,
     |-44-email-100-|,
     10
 )

Animating Changes

To animate a constraint is to change the constant property on it and then call self.layoutIfNeeded() in an animation block.

Animating with stevia is no different than native Autolayout

In both cases, animating the constraint change is as easy as calling layoutIfNeeded in an animation block.

UIView.animateWithDuration(2) {
    self.layoutIfNeeded()
}