Animation not running in the order that code is written - ios

Question

I am trying to set up a button that plays an animation in an image view that's part of my root view controller and then proceed to change the sub view controller.
But for some reason, the code changes the view controller and THEN plays the animation.
I would think that the animation segment would be implemented before the view controller change takes place because, well, it's first in the code.
The code does everything fine, it just does it backwards. Any one have any ideas of what's going wrong?
- (IBAction)next:(UIButton *)sender {
clouds.animationImages = [NSArray arrayWithObjects:
[UIImage imageNamed:#"cloudAnim.0001.png"],
[UIImage imageNamed:#"cloudAnim.0002.png"],
[UIImage imageNamed:#"cloudAnim.0003.png"],
[UIImage imageNamed:#"cloudAnim.0004.png"],
[UIImage imageNamed:#"cloudAnim.0005.png"],
[UIImage imageNamed:#"cloudAnim.0006.png"],
[UIImage imageNamed:#"cloudAnim.0007.png"],
[UIImage imageNamed:#"cloudAnim.0008.png"],
[UIImage imageNamed:#"cloudAnim.0009.png"],
[UIImage imageNamed:#"cloudAnim.0010.png"],
[UIImage imageNamed:#"cloudAnim.0011.png"],
[UIImage imageNamed:#"cloudAnim.0012.png"],
[UIImage imageNamed:#"cloudAnim.0013.png"],
[UIImage imageNamed:#"cloudAnim.0014.png"],
[UIImage imageNamed:#"cloudAnim.0015.png"],
[UIImage imageNamed:#"cloudAnim.0016.png"],
[UIImage imageNamed:#"cloudAnim.0017.png"],
[UIImage imageNamed:#"cloudAnim.0018.png"],
[UIImage imageNamed:#"cloudAnim.0019.png"],
[UIImage imageNamed:#"cloudAnim.0020.png"],
[UIImage imageNamed:#"cloudAnim.0021.png"],
[UIImage imageNamed:#"cloudAnim.0022.png"],
[UIImage imageNamed:#"cloudAnim.0023.png"],
[UIImage imageNamed:#"cloudAnim.0024.png"],
[UIImage imageNamed:#"cloudAnim.0025.png"],
[UIImage imageNamed:#"cloudAnim.0026.png"],
[UIImage imageNamed:#"cloudAnim.0027.png"],
[UIImage imageNamed:#"cloudAnim.0028.png"],
[UIImage imageNamed:#"cloudAnim.0029.png"],
[UIImage imageNamed:#"cloudAnim.0030.png"],
[UIImage imageNamed:#"cloudAnim.0031.png"],
[UIImage imageNamed:#"cloudAnim.0032.png"],
[UIImage imageNamed:#"cloudAnim.0033.png"],
[UIImage imageNamed:#"cloudAnim.0034.png"],
[UIImage imageNamed:#"cloudAnim.0035.png"],
[UIImage imageNamed:#"cloudAnim.0036.png"],
[UIImage imageNamed:#"cloudAnim.0037.png"],
[UIImage imageNamed:#"cloudAnim.0038.png"],
[UIImage imageNamed:#"cloudAnim.0039.png"],
[UIImage imageNamed:#"cloudAnim.0040.png"],
[UIImage imageNamed:#"cloudAnim.0041.png"],
[UIImage imageNamed:#"cloudAnim.0042.png"],
[UIImage imageNamed:#"cloudAnim.0043.png"],
[UIImage imageNamed:#"cloudAnim.0044.png"],
[UIImage imageNamed:#"cloudAnim.0045.png"],
[UIImage imageNamed:#"cloudAnim.0046.png"],
[UIImage imageNamed:#"cloudAnim.0047.png"],
[UIImage imageNamed:#"cloudAnim.0048.png"], nil];
[clouds setAnimationRepeatCount:1];
clouds.animationDuration = 2.0;
[clouds startAnimating];
if (currentPage == 1){
self.page02ViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"page02"];
[self.view insertSubview:_page02ViewController.view atIndex:0];
[self.page01ViewController.view removeFromSuperview];
}
if (currentPage == 2){
self.page03ViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"page03"];
[self.page02ViewController.view removeFromSuperview];
[self.view insertSubview:_page03ViewController.view atIndex:0];
}
currentPage = currentPage +1;
if (currentPage >3){
currentPage = 3;
}
}

Answer 1

Animations are asynchronous, meaning the code below will be executed immediately.
If you want to wait until one loop of the animation has completed, you'll need to delay the code afterward. The simplest way is to use dispatch_after:
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
// Your view controller switching code will be executed after 2 seconds...
});
Beware that, since the method returns immediately, there is nothing stopping the user from hitting the button again and queuing up another transition. You may wish to disable user interaction during the transition, though a 2-second transition will feel like an eternity to the user if they have to switch often.