I'm not sure if this is the most efficient way to do it, but it works..
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.translatesAutoresizingMaskIntoConstraints = NO;
// initialize
[coverForScrolView addSubview:button];
NSLayoutConstraint *width =[NSLayoutConstraint
constraintWithItem:button
attribute:NSLayoutAttributeWidth
relatedBy:0
toItem:coverForScrolView
attribute:NSLayoutAttributeWidth
multiplier:1.0
constant:0];
NSLayoutConstraint *height =[NSLayoutConstraint
constraintWithItem:button
attribute:NSLayoutAttributeHeight
relatedBy:0
toItem:coverForScrolView
attribute:NSLayoutAttributeHeight
multiplier:1.0
constant:0];
NSLayoutConstraint *top = [NSLayoutConstraint
constraintWithItem:button
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:coverForScrolView
attribute:NSLayoutAttributeTop
multiplier:1.0f
constant:0.f];
NSLayoutConstraint *leading = [NSLayoutConstraint
constraintWithItem:button
attribute:NSLayoutAttributeLeading
relatedBy:NSLayoutRelationEqual
toItem:coverForScrolView
attribute:NSLayoutAttributeLeading
multiplier:1.0f
constant:0.f];
[coverForScrolView addConstraint:width];
[coverForScrolView addConstraint:height];
[coverForScrolView addConstraint:top];
[coverForScrolView addConstraint:leading];