How to change bottom layout constraint in iOS, Swift

Take the constraint as IBOutlet of NSLayoutConstraint.

Set the constraint outlets and change constant value by :

self.sampleConstraint.constant = 20self.view.layoutIfNeeded()

If you are adding constraint programatically like this:

var constraintButton = NSLayoutConstraint (item: buttonPlay,                                            attribute: NSLayoutAttribute.Bottom,                                            relatedBy: NSLayoutRelation.Equal,                                            toItem: self.view,                                            attribute: NSLayoutAttribute.Bottom,                                            multiplier: 1,                                           constant: 0)// Add the constraint to the viewself.view.addConstraint(constraintButton)

Then you can update it this way:

self.constraintButton.constant = 50self.view.layoutIfNeeded()

And if you want that with animation you can do it this way:

self.view.layoutIfNeeded()UIView.animateWithDuration(1, animations: {    self.constraintButton.constant = 50    self.view.layoutIfNeeded()})

Hope it helps.

Create an IBOutlet for your constraint:

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *bottomContraint;

And when you need to change it call:

bottomContstraint.constant = //your valueview.layoutIfNeeded()

Also you can animate constraint change like that:

bottomContstraint.constant = //your valueUIView.animateWithDuration(0.5, animations: {  self.view.layoutIfNeeded()})