AutoLayout Modify constraints

Question

I have a problem where I want to modify NSLayoutconstraints on a UIView but it appears a lot of the properties are readonly. I initially have four UIViews as squares in a sort of quad view and they are all tied to each other with a gap of about 20 pixels.

I have a button that increases the frame of one of those squares into full screen encompassing all others. It is at this point I would like to change the constraints of that UIView to attach it to the superviews borders at 20 pixels, that way when I rotate it it doesn't go back to the quad view but maintains full screen. It looks like the property I would want to change is 'seconditem' but this won't work. Am I approaching this problem in the wrong way? I find Autolayout a bit difficult so any help would be much appreciated

Vincent · Accepted Answer · 2015-01-21 18:47:07Z

9

Hi you can do 2 sets of constraints :

1 to manage your quad view with priority High
1 to manage your fullscreen with priority Low

In the method called when you tap your button, set priority high to your fullscreen constraints and priority low to your quad view constraints.

answered Jan 21, 2015 at 18:47

Vincent

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5 Comments

Md1079 Over a year ago

That seems logical, I did get this runtime error though: Mutating a priority from required to not on an installed constraint (or vice-versa) is not supported. You passed priority 250 and the existing priority was 1000

Vincent Over a year ago

Yes, the constraints you want to change priority need not to be "required" (priority = 1000). As I told you, set them to "high" (priority = 750) and switch to "low" (priority = 250), and conversely.

Md1079 Over a year ago

Thanks, gave it a go, but ended up messing other views up (probably due to badly designed constraints)! I ended up just saving and removing all the constraints when the button was pressed and creating a bunch of new ones programatically to get the desired effect. After finished I could just reverse the process.

JerryZhou Over a year ago

I add two constraints for Height(one 0 heigh, another normal) for one view. looks like change their priority can't update the height, to get the hidden & un hidden effect

Anton Tropashko Over a year ago

this is what happens when you are setting priority on constraint: *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Mutating a priority from required to not on an installed constraint (or vice-versa) is not supported. You passed priority 1 and the existing priority was 1000.'

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