iOS: Programmatically change height constraint of a UIView

Question

I wonder is there a way to programmatically retrieve the height constraint of a specific UIView and change its value in the code? I have a situation where I have several UIViews with four edges pinned in the IB and height constraints added (IB complains if I did not), but in the middle of the program I would need to change the height of the UIViews and cause some UIViews to be pushed downward in the view.

I know I can ctrl+drag the height constraints of each UIViews and change their values in the code, but doing so would require me to wire dozens of them. So I think this is not efficient and not scalable in some way.

So I wonder is there a way to totally retrieve the height constraints of a specific view through code and change it dynamically?

Thanks!

Answer 1

First add height constraint to your .h file:

//Add Outlet      IBOutlet NSLayoutConstraint *ViewHeightConstraint; 

Next, add the below code to your .m file:

//Set Value From Here    ViewHeightConstraint.constant = 100; 

Answer 2

You can connect that specific constraint to your code from the interface builder like

And NSLayoutConstraint has a constant property to be set which is your constant pin value.

If you're adding your constraints programmatically, you can surely benefit from the identifier property in NSLayoutConstraint class. Set them and iterate over them to get that specific identifired constraint.

As the documentation says

extension NSLayoutConstraint {     /* For ease in debugging, name a constraint by setting its identifier, which will be printed in the constraint's description.      Identifiers starting with UI and NS are reserved by the system.      */     @availability(iOS, introduced=7.0)     var identifier: String? }