Frames changing suddenly instead of animating [iOS] - ios

Question

I have a view with a scroll view in my app (a percentage calculator). I am trying to animate the view to fly out and then fly in again from the left albeit with different contents, on the press of a button.
Here's my code:
func next()
{
UIView.animateWithDuration(0.5, animations: {
self.mainView.frame = CGRectMake(-500, self.view.bounds.height/2-self.mainHeight/2, self.mainWidth, self.mainHeight)
self.mainView.center.x -= 600
}) { (success) in
self.mainView.center.x += 1200
}
UIView.animateWithDuration(0.5, animations: {
self.mainView.frame = CGRectMake(self.view.bounds.width/2-self.mainWidth/2, self.view.bounds.height/2-self.mainHeight/2, self.mainWidth, self.mainHeight)
}) { (success) in
print("Animation Successful!")
self.drawView()
}
}
I don't understand why, but the animation doesn't occur, the view disappears completely and I see "Animation Successful" in the logs.
To be clear, I have created the view programmatically.
Here's the code in viewDidLoad(); the view displays correctly when it's called:
mainHeight = self.view.bounds.height * 0.85
mainWidth = self.view.bounds.width * 0.85
let viewHeight = self.view.bounds.height
let viewWidth = self.view.bounds.width
mainView.frame = CGRectMake(viewWidth/2-mainWidth/2, viewHeight/2-mainHeight/2, mainWidth, mainHeight)
mainView.layer.cornerRadius = 8
mainView.layer.masksToBounds = true
mainView.backgroundColor = getColor(0, green: 179, blue: 164)
self.view.addSubview(mainView)
scrollView.frame = CGRectMake(0, 0, mainWidth, mainHeight)
scrollView.contentSize = CGSizeMake(mainWidth, 800)
self.mainView.addSubview(scrollView)
contentView.frame = CGRectMake(0, 0, mainWidth, 800);
contentView.backgroundColor = getColor(0, green: 179, blue: 164)
contentView.layer.masksToBounds = true
contentView.clipsToBounds = true
self.scrollView.addSubview(contentView)

Answer 1

Place self.layoutViewIfNeeded() before frame/center changes.
Additionally you may need to put your next animation within a completion handler of the next animation.
func next() {
UIView.animateWithDuration(0.5, animations: {
self.view.layoutIfNeeded() // add this
self.mainView.frame = CGRectMake(-500, self.view.bounds.height/2-self.mainHeight/2, self.mainWidth, self.mainHeight)
self.mainView.center.x -= 600
}) { (success) in
self.view.layoutIfNeeded() // add this
self.mainView.center.x += 1200
// your next animation within a completion handler of previous animation
UIView.animateWithDuration(0.5, animations: {
self.mainView.frame = CGRectMake(self.view.bounds.width/2-self.mainWidth/2, self.view.bounds.height/2-self.mainHeight/2, self.mainWidth, self.mainHeight)
}) { (success) in
print("Animation Successful!")
self.drawView()
}
}
}
I haven't tested it yet, perhaps some changes or lines ordering is needed.

Answer 2

In Swift 3, I had to set the frame and then call layoutIfNeeded().
For example, an animation with spring:
UIView.animate(withDuration: 0.3, delay: 0.1, usingSpringWithDamping: 0.7, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
self.subView.frame = CGRect(x: 0, y: 0, width: 500, height: 200)
self.view.layoutIfNeeded()
}) { (_) in
// Follow up animations...
}