Retina and VFL vs Programmatic Layout

[Luther Baker]

In the following example, I'm displaying a child view in a container view
attached to a view controller's view property ... on a Retina iPhone
simulator.

EXPECTED: The VFL constraints cause the child to fill the screen whereas

UNEXPECTED: the programmatic constraints cause the child to fill exactly
1/4 of the screen (1/2 width, 1/2 height). The programmatic constraints
work if I set the multiplier=2.0 on each of those constraints.

I normally don't use width / height constraints this way but I'm surprised
by the outcome. Is this a Retina pixels/points thing or am I doing
something wrong?

Thanks,
-Luther


//
// 1. Fill the parent view with a simple, yellow container
//
    _containerView = [[UIView alloc] init];
    _containerView.backgroundColor = [UIColor yellowColor];
    _containerView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:_containerView];

    NSArray *cc = [NSLayoutConstraint constraintsWithVisualFormat:@
"V:|[container]|"

options:NSLayoutFormatAlignAllCenterX
                                                          metrics:nil
                                                            views:@{
@"container" : _containerView }];
    [self.view addConstraints:cc];
    cc = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[container]|"

options:NSLayoutFormatAlignAllCenterY
                                                 metrics:nil
                                                   views:@{ @"container" :
_containerView }];
    [self.view addConstraints:cc];

//
// 2. Add a red child to the aforementioned container view
//

    UIView *childView = [[UIView alloc] init];
    childView.backgroundColor = [UIColor redColor];
    childView.translatesAutoresizingMaskIntoConstraints = NO;
    [_containerView addSubview:childView];

// WORKS AS EXPECTED

    cc = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[child]|"

options:NSLayoutFormatAlignAllCenterX
                                                          metrics:nil
                                                            views:@{
@"child" : childView }];
    [_containerView addConstraints:cc];
    cc = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[child]|"

options:NSLayoutFormatAlignAllCenterY
                                                 metrics:nil
                                                   views:@{ @"child" :
childView }];
    [_containerView addConstraints:cc];

//
// now, replace the VFL from above with this and the child view only fills
1/4 of the screen
//

    NSLayoutConstraint *c = [NSLayoutConstraint constraintWithItem:childView

attribute:NSLayoutAttributeWidth

relatedBy:NSLayoutRelationEqual

toItem:_containerView

attribute:NSLayoutAttributeWidth
                                                        multiplier:1.0
                                                          constant:0.0];
    [_containerView addConstraint:c];

    c = [NSLayoutConstraint constraintWithItem:childView
                                     attribute:NSLayoutAttributeHeight
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:_containerView
                                     attribute:NSLayoutAttributeHeight
                                    multiplier:1.0
                                      constant:0.0];
    [_containerView addConstraint:c];
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