How can I change constraints priority in run time

Question

I have a view which has dynamic height and I am trying to change this view height priority in run time.

Here is my part of code;

if (index == 0) {

          


        

Answer 1

I want to make a small addition to Cyrille's answer.

If you are creating constraint in code, make sure to set its priority before making it active. For instance:

surveyViewHeightConstraint = [NSLayoutConstraint constraintWithItem:self
                                               attribute:NSLayoutAttributeHeight
                                               relatedBy:NSLayoutRelationEqual
                                                  toItem:self.superview
                                               attribute:NSLayoutAttributeHeight
                                              multiplier:1
                                                constant:0];
surveyViewHeightConstraint.active = YES;
surveyViewHeightConstraint.priority = 999;

This would result in run-time exception.

Mutating a priority from required to not on an installed constraint (or vice-versa) is not supported.

Correct order is:

surveyViewHeightConstraint.priority = 999;
surveyViewHeightConstraint.active = YES;

For Swift version 4+

constraintName.priority = UILayoutPriority(rawValue: 999)