Animation of Views at ViewController Load - ios

Question

I am performing an animation when one of my ViewControllers loads. I am calling it in the viewDidAppear method. It looks like this.
[UIView animateKeyframesWithDuration:2.5f delay:0.0f options:0 animations:^{
[UIView addKeyframeWithRelativeStartTime:0.0f relativeDuration:1.0f animations:^{
CGRect rocketFrame = _rocketImageView.frame;
rocketFrame.origin.y = rocketFinishPosition;
_rocketImageView.frame = rocketFrame;
CGRect flameFrame = _flameImageView.frame;
flameFrame.origin.y = rocketFinishPosition + rocketFrame.size.height - 3;
_flameImageView.frame = flameFrame;
_flameImageView.hidden = false;
CGRect earthFrame = _earthImageView.frame;
earthFrame.origin.y = earthFinishPosition;
_earthImageView.frame = earthFrame;
CGRect moonFrame = _moonImageView.frame;
moonFrame.origin.y = moonFinishPosition;
_moonImageView.frame = moonFrame;
}];
[UIView addKeyframeWithRelativeStartTime:0.0f relativeDuration:0.6f animations:^{
_flameImageView.transform = CGAffineTransformMakeScale(1.f, 1.f);
}];
} completion:nil];
The issue is when I first load the ViewController, the animation plays but then when finished it snaps back to the starting position. However if I navigate away from the ViewController and back again, the animation plays and the changes persist.
My Question
Are my subviews being played out twice?
When can I be certain that my ViewController has finished loading?

Answer 1

Assuming not-autolayout, in the completion block, set the view properties to the final, desired states...
// taking the rocket frame as an example:
CGRect rocketFrame = _rocketImageView.frame; // do this with the other frames, too
[UIView animateKeyframesWithDuration:2.5f delay:0.0f options:0 animations:^{
[UIView addKeyframeWithRelativeStartTime:0.0f relativeDuration:1.0f animations:^{
rocketFrame.origin.y = rocketFinishPosition;
_rocketImageView.frame = rocketFrame;
CGRect flameFrame = _flameImageView.frame;
flameFrame.origin.y = rocketFinishPosition + rocketFrame.size.height - 3;
_flameImageView.frame = flameFrame;
_flameImageView.hidden = false;
CGRect earthFrame = _earthImageView.frame;
earthFrame.origin.y = earthFinishPosition;
_earthImageView.frame = earthFrame;
CGRect moonFrame = _moonImageView.frame;
moonFrame.origin.y = moonFinishPosition;
_moonImageView.frame = moonFrame;
}];
[UIView addKeyframeWithRelativeStartTime:0.0f relativeDuration:0.6f animations:^{
_flameImageView.transform = CGAffineTransformMakeScale(1.f, 1.f);
}];
} completion:^(BOOL finished) {
// do this with the other frames, too
_rocketImageView.frame = rocketFrame;
}];