CODEWITHSUNDEEP
iosxcodeautolayout
inorganik
inorganik

Reputation: 25525

Changing auto-layout constraints at runtime in table cell

I have subclassed a UITableViewCell which has a bunch of buttons and labels created in IB which all have outlets. What I'm trying to do is, depending on the content of the cell, a UIButton needs to move slightly up, or remain in its place. I created an outlet for the constraint which needs to change so that I can change it in code.

Inside cellForRowAtIndexPath, I have the following:

[cell.usernameButton.superview removeConstraint:cell.usernameTopConstraint];
int topDistance;
// code to conditionally change topDistance for constraint is omitted here, results in either 5 or 15

cell.usernameTopConstraint = [NSLayoutConstraint constraintWithItem:cell.usernameButton
                                                               attribute:NSLayoutAttributeTop
                                                               relatedBy:NSLayoutRelationEqual
                                                                  toItem:cell.usernameButton.superview
                                                               attribute:NSLayoutAttributeTop
                                                              multiplier:1
                                                                constant:topDistance];

[cell.usernameButton.superview addConstraint:cell.usernameTopConstraint];
[cell.usernameButton.superview layoutIfNeeded];

The problem is, the existing constraint must not get removed, because I get the error: "Unable to simultaneously satisfy constraints" - the two it shows me are the two that can get applied above.

Oddly, when I log cell.usernameButton.superview, it's null for every cell until a cell with the non-default topDistance which throws the constraint error. Then it's set for every cell drawn afterwords.

Why isn't the constraint getting removed? I've tried a bunch of different ways of referencing the button's superview, none of which seem to work.

Upvotes: 2

Views: 899

Answers (1)

jrturton
jrturton

Reputation: 119242

Why don't you change the constant instead of removing and re-adding the constraint?

cell.usernameConstraint.constant = topDistance;

Upvotes: 1

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