[SOLVED] Anchor constraint shrinks superview instead of enlarging subview

Anchor constraint shrinks superview instead of enlarging subview

A custom view is located in IB by dragging UIView object from library and it's class name is set to the custom view class name. This custom view has a subview, which is added in init?(coder aDecoder: NSCoder).

How should anchor type constraints be composed, and where should they be located so the _centralLabel subview is set centrally in the custom view, and it's dimensions are 25% of the custom's view dimensions?

If the code is written like this:

override func updateConstraints() {
    if !_subviewsConstraintsAdded {
        _centralLabel.heightAnchor.constraint(equalTo: heightAnchor, multiplier: 0.25).isActive = true
        _centralLabel.widthAnchor.constraint(equalTo: widthAnchor, multiplier: 0.25).isActive = true
        _centralLabel.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true
        _centralLabel.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
        _subviewsConstraintsAdded = true
    }
    super.updateConstraints()
}

The result of the code is, that instead of setting the size of _centralLabel to be 25% of the custom view, the custom view is shrunk to (0,0) which is the size of _centralLabel while updateConstraints() is being called.

Solution

The missing bit was that:

_centralLabel.translatesAutoresizingMaskIntoConstraints = false

which should be located somewhere after programmatically instantiating the subview with this line:

_centralLabel = UILabel()

After this correction the _centralLabel subview has enlarged and has moved to the center of the view, while the view itself remained in its original size, shape and position.