Change UIView location with NSLayoutConstraint

Question

I'm trying to change the location of a UIView with NSLayoutConstraint, but it seems my constraint is not having an effect.

Here is my code:

var view = UIView(frame: CGRectMake(10, 10, 50, 50))
self.view.addSubview(view)
let topConstraint = NSLayoutConstraint(item: view, attribute: .Top, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1.0, constant: 0)
self.view.addConstraint(topConstraint)

The example seems trivial, but I need these constraints to work for something I'm doing later on. Why doesn't this work and how should I be thinking about this differently?

Thanks!