Basic Core Animation - moving image - ios

Question

NO UIVIEW ANIMATIONS, I'M LEARNING CORE ANIMATION
When I run this code, the top image is not on the screen. Then 4 seconds later, it reappears and does as expected. Not sure why. What I want is for the top image to be on the screen when the app launches, and then 4 seconds later for the top image to move up and out of the screen.
#IBOutlet var top: UIImageView!
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
let openTop = CABasicAnimation(keyPath: "position.y")
openTop.fromValue = self.top.frame.origin.y
openTop.toValue = -self.view.bounds.size.height
openTop.duration = 1.0
openTop.beginTime = CACurrentMediaTime() + 4
self.top.layer.addAnimation(openTop, forKey: nil)
self.top.layer.position.y = -self.view.bounds.size.height
}
Any thoughts?

Answer 1

Here's what I came up with:
let l = top.layer!
let startingPosition = l.position
l.position = CGPointMake( CGRectGetMidX( self.view.bounds ), -l.frame.height * 0.5 )
l.addAnimation({
let anim = CABasicAnimation( keyPath: "position" )
anim.fromValue = NSValue( CGPoint:startingPosition )
anim.beginTime = CACurrentMediaTime() + 4.0
anim.fillMode = kCAFillModeBoth
return anim
}(), forKey: nil)

Answer 2

so you want the image to be on-screen at the start, and then 4 seconds later to fly off the top? You can do this by grouping animations together
override func viewDidAppear(animated: Bool)
{
super.viewDidAppear(animated)
// keep a track of where we want it to be
let y = self.top.layer.position.y
// move it out of the way - this where it will end up after the animation
self.top.layer.position.y = -self.view.bounds.size.height
// do nothing, other than display the image for 4 seconds
let doNothing = CABasicAnimation(keyPath: "position.y")
doNothing.fromValue = y
doNothing.toValue = y
doNothing.duration = 4.0
// zip it away
let openTop = CABasicAnimation(keyPath: "position.y")
openTop.fromValue = y
openTop.toValue = -self.view.bounds.size.height
openTop.duration = 1.0
openTop.beginTime = doNothing.beginTime + doNothing.duration
// create the group
let group = CAAnimationGroup()
group.duration = 5.01
group.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseOut)
group.removedOnCompletion = false
group.fillMode = kCAFillModeForwards
group.animations = [doNothing, openTop]
self.top.layer.addAnimation(group, forKey: nil)
}