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

I've found another way to do this. This methodology can be applied anywhere, has no scaling problems; and handles the margins as well. And you don't need 3rd party things for it.

First, dont use this layout:

V:|-?-[Label1]-10-[Label2]-10-|
H:|-?-[Label1]-?-|
H:|-20-[Label2]-20-|

Use these instead:

("|" is the real (outer) container)
V:|-?-[Label1]-0-[Label2HideableMarginContainer]-0-|
H:|-?-[Label1]-?-|
H:|-0-[Label2HideableMarginContainer]-0-|

("|" is Label2HideableMarginContainer)
V:|-10-[Label2]-10-|
H:|-20-[Label2]-20-|

So what have we done now? Label2 is not directly used in the layout; it's placed into a Margin-Container. That container is used as a proxy of Label2, with 0 margins in the layout. The real margins are put inside of the Margin-Container.

Now we can hide Label2 with:

• setting Hidden to YES on it

AND

• Disabling the Top, Bottom, Leading and Trailing constraints. So seek them out, than set Active to NO on them. This will cause the Margin-Container to have a Frame Size of (0,0); because it does have subview(s); but there aren't any (active) layout constraints which anchors those subviews to it.

Maybe a bit complex, but you only have to develop it once. All the logic can be put into a separate place, and be reused every time you need to hide smg.

Here is C# Xamarin code how to seek those constraints which anchors the subview(s) to the inner edges of the Margin-Container view:

public List SubConstraints { get; private set; }

private void ReadSubContraints()
{
    var constraints = View.Constraints; // View: the Margin-Container NSView
    if(constraints?.Any() ?? false)
    {
        SubConstraints = constraints.Where((NSLayoutConstraint c) => {
            var predicate = 
                c.FirstAttribute == NSLayoutAttribute.Top ||
                c.FirstAttribute == NSLayoutAttribute.Bottom ||
                c.FirstAttribute == NSLayoutAttribute.Leading ||
                c.FirstAttribute == NSLayoutAttribute.Trailing;
            predicate &= ViewAndSubviews.Contains(c.FirstItem); // ViewAndSubviews: The View and View.Subviews
            predicate &= ViewAndSubviews.Contains(c.SecondItem);
            return predicate;
        }).ToList();
    }
}