OS X Cocoa Auto Layout hidden elements

Question

I am trying to use the new Auto Layout in Lion because it seems quite nice. But I can not find good information about how to do things. For example:

I have two labels:

Answer 1

This is possible with auto layout, but doesn't exactly scale well.

So, taking your example, let's say you have label A, and label B (or button or anything else really). First start by adding a top constraint to the superview for A. Then a vertical spacing constraint between A and B. This is all normal so far. If you were to remove A at this point, B would have ambiguous layout. If you were to hide it, it would still occupy it's space including the space between the labels.

Next you need to add another constraint from B, to the top of the superview. Change the priority on this to be lower than the others (say 900) and then set it's constant to be standard (or other smaller value). Now, when A is removed from it's superview, the lower priority constraint will kick in and pull B towards the top. The constraints look something like this:

The issue comes when you try to do this with a long list of labels.