iOS autolayout constraints refresh

1
votes

Main question : I have three labels (label1, label2, label3) one below the other. How do I align label3 below label1 if, during runtime, label2 is set to hidden or if removed from superview.

Initial View:

Label1
vertical spacing 
Label2
vertical spacing 
Label3

Action:

set Label2.hidden = yes;

Output:

Label1
vertical spacing
Label3

What I have tried is to apply vertical spacing constraints:

  1. between label1 and label2 with some priority
  2. between label2 and label3 with high priority wrt to 3rd constraint
  3. between label1 and label3 with lowest priority

Now when I remove the label2 how do I refresh the constraints or should I keep track of all constraints and remove the 2nd constraint when label2 is hidden?

2
iphoneiosios6autolayout

2 Answers

1
votes

A solution would be to change the height constraint on label2 so that it's zero and then refresh the constraints so that everything moves up. You'd have to make a property of that variable and set it with +(id)constraintWithItem:(id)view1 attribute:(NSLayoutAttribute)attr1 relatedBy:(NSLayoutRelation)relation toItem:(id)view2 attribute:(NSLayoutAttribute)attr2 multiplier:(CGFloat)multiplier constant:(CGFloat)c;

A couple tips:

  • Make sure you remove, change and re-add the constraint from the label, not the label's superview.
  • You can use all of the same values for the existing constraint for the new one with, of course, the exception of the constant which would be 0.

Good luck!

0
votes

Why not just change label3's frame to equal label2 when you set it to hidden?

So add Label3.frame = Label2.frame; after Label2.hidden = YES; and vice versa.