Get rendered bounds of a view in viewDidLoad() - ios

Question

I've been searching for help on this all day but I can't find an answer.
I have a subview in which I am drawing a rectangle, the rectangle is framed by the subview so I need to know the size of the subview as adjusted by autolayout to correctly frame it. I can't find a way of doing this from ViewDidLoad(), so that the rectangle is correctly rendered at start-up. I have tried the following:
Using dayView.setNeedsLayout() followed by dayView.layoutIfNeeded() before I draw the rectangle in viewDidLoad() but a check either side of these statements shows the dayView.bounds unchanged.
Drawing the view from viewDidLayoutSubviews(), which works, but results in my rectangle being drawn 5 times as viewDidLayoutSubviews() is called for every subview (I have 5 of them) that is redrawn (the relevant subview containing the rectangle is redrawn on call 4 of 5) - this seems wasteful of resources, surely there is a better way?
Drawing the view twice within ViewDidLoad(), hoping the first forced draw will cause the view to be resized, so the second draw will have access to the new bounds after the first draw (desperate I know, but it still doesn't work).
I hope someone can help.
func drawGradient(object: UIView, rect: CGRect, slackX: Int, gradWidth: Int, yPos: Int) -> Void {
// the rectangle width and height set to fit within view with x & y border.
let gradientView = UIView(frame: rect)
let gradient = CAGradientLayer()
gradient.frame = gradientView.frame
gradient.colors = getDayGradientLocations().gradientCol
gradient.locations = getDayGradientLocations().gradientLoc
dayView.layer.addSublayer(gradient)
let civilDawn = getTimeAsProportionOfDay(time: tides.civilDawn) * Double(rect.height) + Double(yPos)
let path = UIBezierPath()
path.move(to: CGPoint(x: slackX, y: Int(civilDawn)))
path.addLine(to: CGPoint(x: slackX + Int(rect.width), y: Int(civilDawn)))
let shapeLayer = CAShapeLayer()
shapeLayer.path = path.cgPath
shapeLayer.strokeColor = UIColor.red.cgColor
shapeLayer.lineWidth = CGFloat(2)
let civilDusk = getTimeAsProportionOfDay(time: tides.civilDusk) * Double(rect.height) + Double(yPos)
path.move(to: CGPoint(x: slackX, y: Int(civilDusk)))
path.addLine(to: CGPoint(x: slackX + Int(rect.width), y: Int(civilDusk)))
shapeLayer.path = path.cgPath
shapeLayer.strokeColor = UIColor.red.cgColor
shapeLayer.lineWidth = CGFloat(2)
object.layer.addSublayer(shapeLayer)
drawLabel(object: object, rect: rect, slackX: slackX, offset: 15, time: tides.civilDawn)
drawLabel(object: object, rect: rect, slackX: slackX, offset: -15, time: tides.civilDusk)
}

Answer 1

A couple of observations:
If you are adjusting a view’s frame in your view controller, the right place to do this is in viewDidLayoutSubviews. Yes, this is called a number of times, but it generally doesn’t have any observable impact on performance.
I wouldn't advise any of those extremely brittle techniques of setNeedsLayout, layoutIfNeeded, or DispatchQueue.main.async inside viewDidLoad. The viewDidLayoutSubviews is the right place if you’re going to do this in the view controller.
Generally, if doing custom subview drawing and layout of subviews, you do this in the layoutSubviews of the view, rather than in any of the view controller methods.
Likewise, if you're doing any manual drawing, you’d put that in the UIView subclass (or any of the relevant CALayer subclasses), not the view controller.
Even better, rather than adjusting frames manually, it’s better to let the auto layout system handle this for you if you can. If you find yourself manually adjusting a frame, there are generally better patterns.
FWIW, you can define a container view’s constraints to be based upon the size (or intrinsic size) of its subviews (and set the content-hugging and compression-resistance of the relevant views). We often think of auto-layout as a top-down engine, but it works both ways.
If you show us your “drawing” code and/or a screen snapshot or two, we can probably offer more concrete counsel.

Answer 2

Got to main thread in viewDidLoad and Perform action will resolve your issue
DispatchQueue.main.async {
// here you can add anything it will have proper frame
}