I am trying to get a subview's bound size in viewDidLoad: (the canvas.bounds)

Initially I did not use the DispatchQueue.main.async wrapper, and the size is not returned correctly. So by experiment, I wrapped the statement in main thread queue. Then it worked.

I know there is a guideline saying that "UI related operation needs to be placed in main thread". But how does this translates into actual coding rule of thumb:

1. If I am just querying a UI property, like getting bounds size, do I need to wrap it inside main thread queue?

2. If I am changing a UI property, e.g. change the bounds size, do I need to wrap it inside the main thread queue? (likely yes I guess)

   override func viewDidLoad() {
   super.viewDidLoad()
   // Do any additional setup after loading the view, typically from a nib.
   
   // stack views
   view.addSubview(photoView)
   view.addSubview(canvas)
   
   DispatchQueue.main.async {
       self.canvas.startPoint = CGPoint.zero
       self.canvas.endPoint = CGPoint(x: self.canvas.bounds.width / 2.0, y: self.canvas.bounds.height)
   
       self.canvas.setNeedsDisplay()
   }
   

Actually this leads to another question I want to ask naturally: having to wrap code in dispatch main looks “unclean”. If u have to wrap it , doesn’t it mean ‘viewDidLoad’ is not the correct life cycle to use? There should be a more appropriate life cycle that doesn’t require dispatch main wrapper?