iOS - changing constraint relation programmatically

Question

given the following constraint in ios programmatically:

IBOutlet NSLayoutConstraint *myConstraint;

this constraint is linked in interfacebuilder to the following details: enter image description here

How do I change the relation attribute programmatically. I tried to look up for a method called setRelation but I don't see it.

What are you trying to do by changing the relation? There might be an easier way. — chedabob
– chedabob, Commented May 21, 2015 at 18:35

i_am_jorf · Accepted Answer · 2015-05-21 18:33:25Z

17

According to the documentation, relation is read-only.

What you will need to do, I suspect, is to set

self.myConstraint.active = NO;

Then make a new NSLayoutConstraint programmatically using:

+ constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant:

And in the process copying values you want to keep, and replacing the relation.

Then add it to the view hierarchy where appropriate.

answered May 21, 2015 at 18:33

i_am_jorf

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Erhan Demirci · Accepted Answer · 2015-07-18 11:52:07Z

4

You can do like that :

  [self.view addConstraint:[NSLayoutConstraint
                                 constraintWithItem:self.yellowView
                                 attribute:NSLayoutAttributeWidth
                                 relatedBy:NSLayoutRelationEqual
                                 toItem:self.redView
                                 attribute:NSLayoutAttributeWidth
                                 multiplier:0.75
                                 constant:0.0]];

answered Jul 18, 2015 at 11:52

Erhan Demirci

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