How to change Auto Layout constraints after they are set when using constraintEqualToAnchor()?

Question

I try to set up a view with AutoLayout constraints by using constraintEqualToAnchor():

override func viewDidLoad() {
    super.viewDidLoad()

    le         


        

Answer 1

// method myView.topAnchor.constraintEqualToAnchor creates new one inactive anchor 
// and not returns exist with equal relationships     

// you can set identifier for any constraint in Interface Builder or code and find & update in code
for ( NSLayoutConstraint *c in [self.view constraintsAffectingLayoutForAxis:UILayoutConstraintAxisHorizontal] )
{
    if ( YES == [c.identifier isEqualToString:@"my.layout-constraint.id"] )
    {
        // Unlike the other properties, the constant can be modified
        // after constraint creation. 
        // Setting the constant on an existing constraint performs much better 
        // than removing the constraint and adding a new one that's exactly like 
        // the old except that it has a different constant.

        c.constant = 123;

        // if needed
        // [self.view setNeedsUpdateConstraints];

        break;
    }
}