ios auto-layout: Programmatically set width constraint

Question

I am working on an ios application. I am adding the auto-layout programmatically to 2 labels.

I need to add a constraint to make them equal width.

I know how to fix the width of a label by using :

constraint = [NSLayoutConstraint
    constraintWithItem:myLabel
             attribute:NSLayoutAttributeWidth
            relatedBy:NSLayoutRelationEqual
              toItem: nil
           attribute:NSLayoutAttributeNotAnAttribute
          multiplier:1.0f
            constant:200.0f];

That would fix the label size to a constant. But I have 2 labels and I want them to have equal size without having to set a constant.

Sebastian Suchanowski · Accepted Answer · 2013-11-29 13:28:50Z

16

It turned out I just have to do the following:

constraint = [NSLayoutConstraint
    constraintWithItem:myLabel
        attribute:NSLayoutAttributeWidth
        relatedBy:NSLayoutRelationEqual
          toItem: otherLabel
       attribute:NSLayoutAttributeWidth
      multiplier:1.0f
        constant:0];

edited Nov 29, 2013 at 13:28

Sebastian Suchanowski

1633 silver badges7 bronze badges

answered Jul 5, 2013 at 22:56

Y2theZ

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4 Comments

Van Du Tran Over a year ago

why do you need a toItem: otherLabel?

Y2theZ Over a year ago

the idea is to make the "myLabel" and "otherLabel" equal width. so I put one of them in the "withItem" and the other in the "otherItem"

Van Du Tran Over a year ago

what if I just want to add a width constrains to myLabel only? what would I put for "toItem". I tried nil but that doesn't do much. Thanks

Y2theZ Over a year ago

@VanDuTran you have to put the toItem: nil and specify the wanted size in the constant. example constant: 100 . if you are having problems you can post a new SO question and you will get answers for it.

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