Getting an existing NSLayoutConstraint for the width?

Question

I\'m trying to animate a control in Cocoa with auto layout.

Now, I can set [[constraint animator] setConstant:newWidth];, which works. But how can I get the

Answer 1

I wrote a reusable extension: (Swift 4.1)

/**
 * Utils when working with constraints
 */
extension NSLayoutConstraint{
    /**
     * Returns all constraints of kinds
     * EXAMPLE: NSLayoutConstraint.ofKind(rect.immediateConstraints, kinds: [.width,.height]) //width, height
     */
    static func ofKind(_ constraints:[NSLayoutConstraint],kinds:[NSLayoutAttribute]) -> [NSLayoutConstraint]{
        return kinds.map { kind in
            return constraints.filter { constraint in
                return constraint.firstAttribute == kind
            }
        }.flatMap({$0})//flattens 2d array to 1d array
    }
}