以编程方式编辑NSLayoutConstraint常量吗？

Question

I have an NSLayoutConstraint with an IBOutlet connected. In my XIB the constraint has a constant value an several others for specific layouts. For example, Compact Width x Any Height.

Programmatically I know I can edit the constant like so:

myConstraint.constant = 10;

However, I want to edit the additional constants for the various layouts. How can I do this?

Answer 1

You can use install and uninstall feature. For example let say we have a width constraint which is install in hAny/wCompact and we create IBOulet for this constraint. Then it will have affect on hAny/wCompact. Then we can go to other size class say hCompact/wCompact. and Make previous constraint uninstall and create a new width constraint in hComp/wComp. We can create a new IBOutlet for the newly created constraint. And it has affect on hComp/wComp.

myConstraintInOneSizeClass.constant = 10;
myConstraintInOtherSizeClass.constant = 20;

They are install in their own size classes

Install and uninstall a constraint for different size classes:

https://developer.apple.com/library/ios/recipes/xcode_helpIB_adaptive_sizes/chapters/EnableAndDisableConstraints.html

Hope it can help.