iOS 8 - Find constraints for a UIView with identifier

Question

I am trying to change a constraint for an ImageView for iPhone 4S,5,5S in viewDidLoad:

for (NSLayoutConstraint *constraint in logoImage.constraints) {
    if ([constraint.identifier isEqualToString:@"logoTopIdentifier"]) {
        constraint.constant=10;
    }
}

It seems that it's not even iterating in the loop. Is there any other way to get a specific constraint with identifier?

Answer 1

You can connect the constraint in storyboard to your view controller class same as connecting a UI element.

Just find the constraints in your storyboard, make the workspace into split view, and drag the constraint to your corresponding view controller class.

Sometimes if you want to animate the position change, you can update the constraint like:

self.theConstraint?.constant = 100 
self.view.setNeedsUpdateConstraints()
UIView.animateWithDuration(0.7) { () -> Void in
    self.view.layoutIfNeeded()
}

block.

That is it.

Answer 2

Here is the KVConstraintExtensionsMaster library by which you can access the any constant from a view based on the NSLayoutAttribute. No matter whether that constraint added Programmatically or from Interface Builder.

 [self.logoImage accessAppliedConstraintByAttribute:NSLayoutAttributeTop completion:^(NSLayoutConstraint *expectedConstraint){
        if (expectedConstraint) {
            expectedConstraint.constant = 10;

            /* for the animation */ 
            [self.logoImage  updateModifyConstraintsWithAnimation:NULL];
      }
    }];