UIView动画被跳过

Question

Ok quick background: I am seguing between two controllers: my home controller and a controller that has a map as view. A segue is triggerd when the user clicks on the textField of the search bar

I have included images of before and after animation

The process goes as:

I add the search bar to let keyWindow = UIApplication.shared.keyWindow at the same position as it was in the table view

let preLeadingConstraint = searchView.leadingAnchor.constraint(equalTo: keyWindow.leadingAnchor, constant: 8)
let preTrailingConstraint = searchView.trailingAnchor.constraint(equalTo: keyWindow.trailingAnchor, constant: -8)
let preTopConstraint = searchView.topAnchor.constraint(equalTo: keyWindow.topAnchor, constant: originY)

NSLayoutConstraint.activate([preLeadingConstraint, preTrailingConstraint, preTopConstraint])
keyWindow.layoutIfNeeded()

No problem here. Also: the search bar has a height constraint activated before that: heightAnchor.constraint(equalToConstant: PlacesSearchView.height).isActive = true

Next step is this animation (custom segue):

UIView.animate(withDuration: self.duration, animations: {
    homeController.view.frame.origin.x = -Global.width
    self.destination.view.frame.origin.x = 0
}) { _ in
    homeController.navigationController?.viewControllers.append(self.destination)
    self.destination.navigationController?.setNavigationBarHidden(false, animated: true)
}

Very straightforward and again no problem

This part is the issue:

I deactivate the old search bar constraints:

NSLayoutConstraint.deactivate(preConstraints)

I create the close button and anchor it to keyWindow:

let side: CGFloat = 25
let margin: CGFloat = 8

closeButton?.topAnchor.constraint(equalTo: keyWindow.layoutMarginsGuide.topAnchor, constant: margin).isActive = true
closeButton?.centerXAnchor.constraint(equalTo: keyWindow.centerXAnchor).isActive = true
closeButton?.heightAnchor.constraint(equalToConstant: side).isActive = true
closeButton?.widthAnchor.constraint(equalTo: closeButton!.heightAnchor).isActive = true

Then I apply new constraints to the Search Bar.

topAnchor.constraint(equalTo: closeButton!.bottomAnchor, constant: yAxisMargin).isActive = true
leadingAnchor.constraint(equalTo: keyWindow.leadingAnchor, constant: 0).isActive = true
trailingAnchor.constraint(equalTo: keyWindow.trailingAnchor, constant: 0).isActive = true

And anchor to keyboard:

bottomKeyboardConstraint = bottomAnchor.constraint(equalTo: keyWindow.bottomAnchor, constant: -keyboardHeight)
heightConstraint.isActive = false
bottomKeyboardConstraint?.isActive = true

instantiateTableView()
subviewTableView()

Then of course I apply the magic formula:

UIView.animate(withDuration: 0.5, animations: {
    keyWindow.layoutIfNeeded() 
    // (I also animate background color)
}

BUT! To my surprise... it skips the animations. Goes straight to end state. Like straight to picture 2. I tried to do (silly) stuff to have some kind of animation going one (like for example I tested with a simplified version of this: did not add nor deactivate any constraint and just tried changing topConstraint.constant to 0 and... same thing: the search bar goes straight up without any animation)

What am I not getting? Thanks for bearing with my answer and I look forward to your insights!

Update: For some reason I have forgotten to put the last UIView.animate block in a DispatchQueue.main.async block. Doing so results in... having an animation sometimes and no animations most of the time. This is becoming increasingly weird. Also, I never had to put any of my animations in a DispatchQueue.main.async block prior to that, even in other custom segues, which is also weird.

Answer 1

Ok I got it, here is what's happening:

Basically... DispatchQueue.main.async was the root of the problem. Let me explain.

First off, let's be clear, I perform the segue inside a DispatchQueue.main.async block:

DispatchQueue.main.async {
     self.performSegue(withIdentifier: HomeViewController.storyboardData.segueIdentifiers.places, sender: self)
}

But apparently... it is not enough.

I then had the idea of placing my override func perform() code inside a DispatchQueue.main.async (yes again... I know!). So it looked like this:

override func perform() {
    DispatchQueue.main.async {
        ...
    }
}

And... it was animating every time!

The animations were weird so I basically decided to try placing different portions of code in the block till it'd work and... it eventually worked. (Kind of a shame to do this sort of thing I'll admit). Now for those interested the details are as follow:

• There is a portion of code responsible of animating in case the user clicked the searchButton. This worked prior to placing the whole perform() code inside a DispatchQueue.main.async block so... I rolled back to the working version

• Now for the portion responsible of animating in case the user clicked the textField: It basically looks like this now (segueToEditing is where I create the closeButton, delete old constraint, add the new ones and animate):

  DispatchQueue.main.async { self.segueToEditing() }

I am still kind of confused by how my solution works, but I now know that I shall not mess with DispatchQueue.main.async blocks.