从子视图调用UIView.animate不起作用

Question

I'm playing around trying to get familiar with swift4 and xcode. I have created a container view which id like to toggle the width on with UIView.animate from the child view.

If I call my toggleWidth function from the containers view controller class, it animates.

If I call it from the child view controller, it changes width, but does not animate.

Can someone explain why?

Here is the relevant code:

Container Controller

class ViewController: UIViewController {
  @IBOutlet weak var menuContainer: UIView!
  @IBOutlet weak var menuWidth: NSLayoutConstraint!

  override func viewDidLoad() {
    super.viewDidLoad()

    toggleMenu()
  }

  func toggleMenu() {
    menuWidth.constant -= 100

    UIView.animate(withDuration: 5) {
        self.menuContainer.layoutIfNeeded()
    }
  }
}

Child Controller

class MenuController : UITableViewController {
  @IBOutlet weak var homeCell: UITableViewCell!

  override func viewDidLoad() {
    let tap = UITapGestureRecognizer(target: self, action: #selector(MenuController.imageTapped))
    homeCell.addGestureRecognizer(tap)
    homeCell.isUserInteractionEnabled = true
  }

  @objc func imageTapped()
  {
    (self.parent as! ViewController).toggleMenu()
  }
}

Appreciate any help that can be given on this one.

Answer 1

The change to width needs to be done within the animation block, as mentioned in https://developer.apple.com/documentation/uikit/uiview/1622418-animate .

class ViewController: UIViewController {
  @IBOutlet weak var menuContainer: UIView!
  @IBOutlet weak var menuWidth: NSLayoutConstraint!

  override func viewDidLoad() {
    super.viewDidLoad()

    toggleMenu()
  }

  func toggleMenu() {
    UIView.animate(withDuration: 5) {
       self.menuWidth.constant -= 100
       self.menuContainer.layoutIfNeeded()
    }
  }
}

Answer 2

ok, ive gotten back to this after playing with a simple test project, I realised i was calling layoutifneeded on the view i was changing the constraint on, whereas apple clearly state you should call layoutifneeded on the parent object. once i changed this, everything started working a charm. hope someone can learn from my mistake.