The Way The Way - 3 months ago 13
iOS Question

Why is constraint not working for UIView but works for UILabel?

I have a simple (complete) example here which seems very odd, but surely im just missing something small... right? Can you help debug the simple code below. This code makes the aView disappear, but when if I put the aLabel in the constraint where the aView is, it works perfect. Why? Thanks for any input, this seems crazy to me.

austin

UIView *aView = [[UIView alloc] initWithFrame:CGRectMake(0, 100, 100, 30)];
aView.backgroundColor = [UIColor redColor];
aView.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:aView];

UILabel *aLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 100, 100, 30)];
aLabel.backgroundColor = [UIColor redColor];
aLabel.text = @"Label";
aLabel.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:aLabel];

NSLayoutConstraint *myConstraint =[NSLayoutConstraint
constraintWithItem:aView
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeCenterY
multiplier:1.0
constant:0];

[self.view addConstraint:myConstraint];

myConstraint =[NSLayoutConstraint
constraintWithItem:aView
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeCenterX
multiplier:1.0
constant:0];

[self.view addConstraint:myConstraint];

Answer

Well, the line aView.translatesAutoresizingMaskIntoConstraints = NO; is making the view's size zero.. So you got to add these lines of code :

NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:aView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:100];
[aView addConstraint:widthConstraint];


NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:aView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];
[aView addConstraint:heightConstraint];