Update height constraint programmatically

Instead of adding a new constraint, you need to modify the constant on your existing constraint.

Use an IBOutlet to connect to your constraint in Interface Builder:

@property (nonatomic, weak) NSLayoutConstraint *heightConstraint;

Then, when you need to set it programmatically, simply set the constant property on the constraint:

heightConstraint.constant = 100;

OR

If you can't access the nib in Interface Builder, find the constraint in code:

NSLayoutConstraint *heightConstraint;for (NSLayoutConstraint *constraint in myView.constraints) {    if (constraint.firstAttribute == NSLayoutAttributeHeight) {        heightConstraint = constraint;        break;    }}heightConstraint.constant = 100;

And in Swift:

if let constraint = (myView.constraints.filter{$0.firstAttribute == .width}.first) {            constraint.constant = 100.0        }

To get a reference of your height constraints :Click + Ctrl in the constraint and drag and drop in your class file :

To update constraint value :

self.heightConstraint.constant = 300;[self.view updateConstraints];

A more flexible way using this swift extension:

extension UIView {        func updateConstraint(attribute: NSLayoutAttribute, constant: CGFloat) -> Void {        if let constraint = (self.constraints.filter{$0.firstAttribute == attribute}.first) {            constraint.constant = constant            self.layoutIfNeeded()        }    }}

How to use this view extension to update constant value of existing constraints:

// to update height constanttestView.updateConstraint(attribute: NSLayoutAttribute.height, constant: 20.0)// to update width constanttestView.updateConstraint(attribute: NSLayoutAttribute.width, constant: 20.0)