Stopping performSelectorInBackground - objective-c

Question

In objective-c, when a button is pressed, I load a processing animation while a file is uploaded using:
[self performSelectorInBackground:#selector(loadAnimation) withObject:self];
This works and a loadAnimation image displays.
How do I stop it once the file has uploaded? I have tried:
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(loadAnimation) object:nil];
But this does not stop the animation.
The loadAnimation is:
- (void) loadAnimation
{
loadingPng.hidden=NO;
NSArray *imageArray = [[NSArray alloc] initWithObjects:[UIImage imageNamed:#"0.png"], [UIImage imageNamed:#"1.png"], [UIImage imageNamed:#"2.png"], [UIImage imageNamed:#"3.png"], [UIImage imageNamed:#"4.png"], [UIImage imageNamed:#"5.png"], nil];
loadingPng = [[UIImageView alloc] initWithFrame:CGRectMake(487, 500, 50, 50)];
[self.view addSubview:loadingPng];
loadingPng.animationImages = imageArray;
loadingPng.animationDuration = 1.5;
[loadingPng startAnimating];
}

Answer 1

Just to make things clear performSelectorInBackground creates another thread, which executes the method and dies (if not attached to any runloop).
If during this execution something on the screen appears and you want to hide it, just call a whatever routine needed to hide it. If you use UIActivityIndicatorView or UIImageView call -(void)stopAnimating (in this case [loadingPng stopAnimating]).
There is no need in starting animation in background, actually it's a thing that should not be done, because anything that involves UI manipulation is highly recommended to be done only on the main thread.
It's a loading that should go to background, and animation triggering stays on the main thread.