Increasing frame.origin.x vs constant - ios

Question

I'm trying to understand how iOS frame and bounds works.
I put an subView:UIView on UIViewController and a button which can increase subView's frame origin coordinate and change textlabel with its value.
like this,
let subView: UIView = UIView(frame: CGRect(x: 50, y: 50, width: 100, height: 100))
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(subView)
subView.backgroundColor = .blue
}
#IBAction func btnMoveBottomView(_ sender: Any) {
subView.frame.origin.y = subView.frame.origin.y + 100
lbFrameInfo.text = String(format:"sub = (%.1f, %.1f)", subView.frame.origin.x, subView.frame.origin.y)
self.view.setNeedsLayout()
self.view.layoutIfNeeded()
}
After I make this action, I see subView go down but text doesn't change.
on debug console I see this change
po subView.frame.origin
▿ (50.0, 2350.0)
- x : 50.0
- y : 2350.0
updateViewConstraints has been called too.
override func updateViewConstraints() {
print("updateViewConstraints")
super.updateViewConstraints()
}
Instead of increasing frame.origin.x like this, increasing value of leading constant works perfectly.
It would be appreciated if someone can guide me the differences of these and the concept of frame and if it is related with auto-layout things

Answer 1

According to your question,
You have added subView to ViewController view so when u create view
let subView: UIView = UIView(frame: CGRect(x: 50, y: 50, width: 100, height: 100))
and do this
view.addSubview(subView)
it means your subview will be at 50 position down and away from left of the screen.
so when u do this.
subView.frame.origin.y = subView.frame.origin.y + 100
it will move your frame further down in the screen as you are changing the y position of frame which is the starting position of creating your view on screen.
At its simplest, a view’s bounds refers to its coordinates relative to its own view (as if the rest of your view hierarchy didn’t exist), whereas its frame refers to its coordinates relative to its parent’s view. Frame will reflect the position in its parents view.
This means a few things:
1.If you create a view at X:0, Y:0, width:100, height:100, its frame and bounds are the same.
2.If you move that view to X:100, its frame will reflect that change but its bounds will not. Remember, the bounds is relative to the view’s own space, and internally to the view nothing has changed.
3.If you transform the view, e.g. rotating it or scaling it up, the frame will change to reflect that, but the bounds still won’t – as far as the view is concerned internally, it hasn’t changed
hope it clears your doubts