UITextField subclass with bar underneath: bar not going all the way - ios

Question

The objective
I've made my own UITextField subclass, to design it in such a way that there is no border, only a white line under the text. (Subclass code below)
The issue
Unfortunately, the white line does not go to the end of the text field (in terms of width):
I've constrained the text field to have 0 px distance to both the left and right edges of the view, but as the images below show, the line does not meet those constraints.
My investigation and hypotheses
I've put in quite some time to debug, the only thing I can think of is that the dimensions specified in the code (copied below) are exécute before the constraints are applied to the view, which is not something I know how to resolve.
The code
//In a UITextField subclass
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
public override func awakeFromNib() {
super.awakeFromNib()
setup()
}
func setup() {
self.delegate = self
// BORDER
// Remove rectangular border
self.borderStyle = .none
self.layer.borderColor = UIColor(red: 1, green: 1, blue: 1, alpha: 0).cgColor //Make transparent
self.layer.borderWidth = 0 // width = 0
// Add bottom border
bottomBorder = UIView(frame: CGRect(x: 0, y: self.frame.height, width: self.frame.width, height: 1))
bottomBorder.backgroundColor = UIColor.white
self.addSubview(bottomBorder)
}

Answer 1

the only thing I can think of is that the dimensions specified in the code (copied below) are exécute before the constraints are applied to the view,
Perfectly correct! The whole problem is that you are hard-coding the frame of the bar based on the frame of the text field. But the frame of the text field is not yet known during init.
Your entire approach here is wrong. You should be using autolayout constraints to constrain the bar to the text field, not giving the bar a fixed frame. That way, no matter what happens to the size of the text field (as it obeys the constraints you have given it), the size of the bar will follow along in perfect harmony.

Answer 2

You need
override func layoutSubviews() {
super.layoutSubviews()
bottomBorder.frame = CGRect(x: 0, y: self.frame.height - 1, width: self.frame.width, height: 1)
}
As correct frame size of superView is captured inside layoutSubviews not in init / awakeFromNib where the frame is set for current development device dimensions if it's in IB