使用嵌入式视图了解自动布局生命周期和顺序

Question

I have the following view hierarchy:

ViewController: UIViewController 
|
+--- cardViewController: CardViewController (subclass of UIViewController)
     |
     +--- containerView: UIView
          |
          +--- menuTableView: MenuTableView (subclass of UITableView)
          

The CardViewController is shown on the ViewController 's view through the folloing code (called from ViewController):

  let cardViewController = CardViewController(startWithRoundedCorners: true)
  self.addChild(cardViewController)
  self.view.addSubview(cardViewController.view)
  cardViewController.showCard()

In CardViewController , the containerView has constraints to the view's top, leading, trailing, and bottom anchors.

In turn, the menuTableView also has constraints to the containerView s top leading, trailing and bottom anchors.

The issue is this. The menuTableView.contentSize.height is only being calculated after the tableView cells are loaded through cellForRowAt . Makes sense. Up until that point in time, it looks like it's just doing an estimation of the tableView height based on the number of rows * 44 (the default size). So if I check the menuTableView.contentSize.height in CardViewController: viewDidLayoutSubviews() , I get back 264.0 .

I've captured some print statements (with a 'started' and 'finished' for some of the overridden methods) to try and work out the order that things are running in:

CardViewController: setuptableView(): started 
MenuTableView: convenience init(): started 
MenuTableView: override init(): started 
MenuTableView: numberOfRowsInSection: 
MenuTableView: override init(): self.frame.height: 0.0 
MenuTableView: override init(): self.contentSize.height: 0.0 
MenuTableView: override init(): finished 
MenuTableView: convenience init(): self.frame.height: 0.0 
MenuTableView: convenience init(): self.contentSize.height: 0.0 
MenuTableView: convenience init(): finished 
CardViewController: setuptableView(): finished
MenuTableView: numberOfRowsInSection: 
CardViewController: showCard(): self.frame.height: 0.0 
CardViewController: showCard(): self.contentSize.height: 264.0 
CardViewController: updateViewConstraints(): started 
CardViewController: updateViewConstraints(): finished  
CardViewController: viewWillLayoutSubviews(): started 
CardViewController: viewDidLayoutSubviews(): self.frame.height: 0.0 
CardViewController: viewDidLayoutSubviews(): self.contentSize.height: 264.0 
CardViewController: viewWillLayoutSubviews(): finished 
CardViewController: viewDidLayoutSubviews(): started  
CardViewController: viewDidLayoutSubviews(): self.frame.height: 0.0 
CardViewController: viewDidLayoutSubviews(): self.contentSize.height: 264.0 
CardViewController: viewDidLayoutSubviews(): finished 
MenuTableView: numberOfRowsInSection: 
MenuTableView: layoutSubviews(): started 
MenuTableView: numberOfRowsInSection: 
MenuTableView: cellForRowAt indexPath: [0, 0] 
MenuTableView: cellForRowAt indexPath: [0, 1] 
MenuTableView: cellForRowAt indexPath: [0, 2] 
MenuTableView: cellForRowAt indexPath: [0, 3] 
MenuTableView: cellForRowAt indexPath: [0, 4] 
MenuTableView: cellForRowAt indexPath: [0, 5] 
MenuTableView: layoutSubviews(): self.frame.height: 264.0 
MenuTableView: layoutSubviews(): self.contentSize.height: 306.0 
MenuTableView: layoutSubviews(): finished 
MenuTableView: layoutSubviews(): started 
MenuTableView: layoutSubviews(): self.frame.height: 264.0 
MenuTableView: layoutSubviews(): self.contentSize.height: 306.0 
MenuTableView: layoutSubviews(): finished

The code for the CardViewController: showCard() method is:

UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.6, initialSpringVelocity: 1.0, options: .curveEaseInOut, animations: { [weak self] in
    let cardHeight = (self?.menuTableView.contentSize.height)! + self!.cardHandleAreaHeight
    self?.view.frame = CGRect(x: 0, y: (self?.parent?.view.frame.height)! - cardHeight, width: (self?.parent?.view.frame.width)!, height: cardHeight)
    
    }, completion: nil)

So from what I can tell, the problem is that the menuTableView.layoutSubviews gets called, and correctly has the tableView.contentSize.height at 306.0 . But by this stage, the parent viewController ( CardViewController ) has already finished with its viewWillLayoutSubviews and viewDidLayoutSubviews .

Question

How can the parent be finished laying out its subviews when the subviews are actually still laying out their views?? Based on Apple's documentation, they say that the Auto Layout loop is:

1. Update constraints (bottom-up, from subview to superview)
2. Layout (top-down)
3. Drawing/Display

And if changes to the intrinsic content size of, in this case, the tableView cause an update to occur to the auto layout constraints, I'm at a loss why this loop doesn't work. I've played around with a whole bunch of options and there are different ways to trigger it but I'm looking to understand the Auto Layout engine so I stop running into these issues.

Additional Info

Interesting, if I call cardViewController.showCard() a second time, then it is correct. The additional print logs are then:

CardViewController: showCard(): started
CardViewController: showCard(): self.frame.height: 278.0
CardViewController: showCard(): self.contentSize.height: 306.0
CardViewController: showCard(): finished
CardViewController: viewWillLayoutSubviews(): started
CardViewController: viewDidLayoutSubviews(): self.frame.height: 278.0
CardViewController: viewDidLayoutSubviews(): self.contentSize.height: 306.0
CardViewController: viewWillLayoutSubviews(): finished
CardViewController: viewDidLayoutSubviews(): started 
CardViewController: viewDidLayoutSubviews(): self.frame.height: 278.0
CardViewController: viewDidLayoutSubviews(): self.contentSize.height: 306.0
CardViewController: viewDidLayoutSubviews(): finished
MenuTableView: layoutSubviews(): started
MenuTableView: layoutSubviews(): self.frame.height: 306.0
MenuTableView: layoutSubviews(): self.contentSize.height: 306.0
MenuTableView: layoutSubviews(): finished

Happy to make the project file available if that's easier.

Answer 1

sorry i can't add a comment yet so i tried to use this answer section as question.

where did you put these?

let cardViewController = CardViewController(startWithRoundedCorners: true)
  self.addChild(cardViewController)
  self.view.addSubview(cardViewController.view)
  cardViewController.showCard()