Setting view width constraint from custom UIView class not updating frames - swift

Question

I've got a UIView in which I want to have a simple loader view by using a percentage to determine the width.
I've got the percentage code completed and I know it's working.
However I'm having trouble setting the view's width constraint. I find the width by getting the frame width and multiplying it by the percentage. I know it's getting the right width. But I can't seem to set the constraint from this function.
My code goes like this in my UIView subclass:
func initSubviews() {
// in here i do some other stuff and have an asyncronous call to an api
// so then I've got this code calling the next function
DispatchQueue.main.async {
self.setCompletionWidth(nextTimer: nextTimer!, oldDate: oldDate!)
}
}
func setCompletionWidth(nextTimer: Date, oldDate: Date) {
let date = Date()
// calculatePercent returns something like 0.49
let percent = calculatePercent(middleDate: date, endDate: nextTimer, originalDate: oldDate)
//this is returning a correct value
let width = (self.frame.width)*percent
// completionView is the view I'm trying to change the width of
self.completionView.widthAnchor.constraint(equalToConstant: width)
self.layoutSubviews()
}
What's happening is that the completionView isn't getting the right width.
I've also tried in the setCompletionWidth function
self.completionView.widthAnchor.constraint(equalToConstant: width)
containerView.layoutSubviews()
and
UIView.animate(withDuration: 0.2) {
self.completionView.widthAnchor.constraint(equalToConstant: width)
self.containerView.layoutSubviews()
//also tried self.layoutSubviews here
}
and
self.layoutIfNeeded()
self.completionView.widthAnchor.constraint(equalToConstant: width)
self.layoutIfNeeded()
I'm expecting the width of the completionView to be something like 150, but instead it's 350, which is the original width it had.
I think what's happening is the view isn't updating after me setting the constraint to a different value. However, I can't for the life of me get it to update. I'd love some help here.

Answer 1

You need .isActive = true
self.completionView.widthAnchor.constraint(equalToConstant: width).isActive = true
Also to change the width you need to create a width var like
var widthCon:NSLayoutConstraint!
widthCon = self.completionView.widthAnchor.constraint(equalToConstant: width)
widthCon.isActive = true
Then change the constant with
widthCon.constant = /// some value
self.superview!.layoutIfNeeded()