This may not be entirely true, but it feels that way:

Everything looks better with ReactiveCocoa.

I always try to strip my posts from added complexity. In my previous post, I showed an alternative to working with dynamic autolayout without having complex calculations. I didn’t thought it was relevant to introduce ReactiveCocoa or FRP in that mix.

But, as I said before, everything looks better with ReactiveCocoa.

I created a new branch on the original project that you can browse, but here’s the gist of it, we bind each constraint’s priority to the selected position:

let priorityMap: (Position, Position) -> (UILayoutPriority) = {
  $0 == $1 ? UILayoutPriorityDefaultHigh : UILayoutPriorityDefaultLow

self.leftPositionConstraint.rac_priority <~ { priorityMap($0, .Left) }

self.centerPositionConstraint.rac_priority <~ { priorityMap($0, .Center) }

self.rightPositionConstraint.rac_priority <~ { priorityMap($0, .Right) }

self.positionLabel.rac_text <~ { $0.rawValue }

self.position.signal.observeNext { [weak self] _

  // Animate.

All your layout code turned into just four lines. Much better.