How to remove Equal Width constraint from UIButton Programmatically in iOS - ios

Question

I have two button with equal width constraints. I want to remove equal width constraint and add a new width constraint for one button. the other button constraint to zero.
This is what I've tried. But it's not working. The Equal width constraint is not removing
NSLayoutConstraint * constraint = [self
constraintWithIndientifer:#"MyButtonWidth" InView:self.view];
[self.view removeConstraint:constraint];
NSLayoutConstraint * newconstraint = [NSLayoutConstraint constraintWithItem:self.departureButton attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:1 constant:self.view.frame.size.width];
newconstraint.identifier = #"MyButtonWidth";
[self.departureButton addConstraint:newconstraint];
[self.view layoutIfNeeded];
-(NSLayoutConstraint *)constraintWithIndientifer:(NSString *)identifer InView:(UIView *)view{
NSLayoutConstraint * constraintToFind = nil;
for (NSLayoutConstraint * constraint in view.constraints ) {
if([constraint.identifier isEqualToString:identifer]){
constraintToFind = constraint;
break;
}
}
return constraintToFind;
}

Answer 1

You don't need to do this,
you can add another constraint such as width constraint to >=1
after that, you should set "equal constraint" "priority to 1
after that, you should set "width constraint" priority to 2 or more(default is 1000)
after that, when you set constraint constant it works and equal constraint is not working because of priority:
self.yourButtonWidthConstraint.constant = yourWidth;

Answer 2

If you look at the documentation for NSLayoutConstraint, you'll find an isActive property:
You can activate or deactivate a constraint by changing this property. Note that only active constraints affect the calculated layout.
Activating or deactivating the constraint calls addConstraint: and removeConstraint: on the view that is the closest common ancestor of the items managed by this constraint. Use this property instead of calling addConstraint: or removeConstraint: directly.
So going by that I'm changing both the removeConstraint and addConstraint you have in your sample code.
aka just change your code to this:
NSLayoutConstraint * constraint = [self
constraintWithIndientifer:#"MyButtonWidth" InView:self.view];
constraint.active = NO; // CHANGE 1
NSLayoutConstraint * newconstraint = [NSLayoutConstraint constraintWithItem:self.departureButton attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:1 constant:self.view.frame.size.width];
newconstraint.identifier = #"MyButtonWidth";
newConstraint.active = YES; // CHANGE 2
[self.view layoutIfNeeded];
NOTE: the NSLayoutConstraint class also has two class funcs: + activateConstraints: and + deactivateConstraints:, which both take an array of constraints. That's preferred when you're changing multiple constraints, but not needed here since its only 1.

Answer 3

Loop though the constraints of the parent view of these two buttons and delete the constraint where first item is the first button and second is the second button and layoutAttribute is width
for (NSLayoutConstraint*co in self.parentOfBtns.constraints)
{
if(co.firstItem==self.btn1&&co.secondItem==self.btn2&&co.firstAttribute==NSLayoutAttributeWidth&co.secondAttribute==NSLayoutAttributeWidth)
[self.parentOfBtns removeConstraint:co];
}
then add your new width constraint , and don't forget to call
[self.view layoutIfNeeded];