Is it possible to delete/create a constraint

Question

screenshot of constraints

I want to learn if there's a way to delete AND create a constraint

So I have greenTop constrained to viewTop, purpleTop to greenBottom etc...

I want to be able to delete greenTop-viewTop constraint, delete purpleTop-greenBottom...and create a new purpleTop-viewTop constraint and a greenTop-blackBottom. (programmatically)

Effectively moving green to bottom and all others shift up one space.

Note: I know i could just make each constrained to topView and adjust, but I'd like to learn this way.

this was an exercise for myself to learn deleting and addition of constraints — Chameleon
– Chameleon, Commented Apr 16, 2015 at 20:17

rdelmar · Accepted Answer · 2015-03-19 22:06:26Z

1

Sure, you can do that. You can make an IBOutlet to a constraint just like any other object. Call removeConstraint on the owner of that constraint to remove it,

someView.removeConstraint(someConstraint) // someConstraint is an IBOutlet

You cannot change the items or a relationship in a constraint, so #2 will not work.

answered Mar 19, 2015 at 22:06

rdelmar

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3 Comments

rdelmar Over a year ago

@Dustin, what do you mean? How to create a constraint in code? Look at the methods in the NSLayoutConstraint class reference.

Chameleon Over a year ago

ok so I could create all possible constraints and activate/deactivate as need. But I can't understand the constraintsWithVisualFormat in reference, so I guess i could also use the init(item:attribute:relatedBy:toItem:attribute:multiplier:constant:) reference

rdelmar Over a year ago

@Dustin, if you don't understand it, read the document, "Auto Layout Concepts", and watch the videos on auto layout from the 2012 WWDC.

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