Question

I have this method…

- (void) helloThere: (int) myValue {

  // I am trying to pass myValue to animationDidStop
  [UIView beginAnimations:nil context:[NSNumber numberWithInt: myValue]];
  [UIView setAnimationDuration:1.0];
  [UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:context:)];
  [UIView setAnimationDelegate:self];

  // do stuff

  [UIView commitAnimations];
}

then I am trying to retrieve myValue on animationDidStop…

- (void)animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {

  int retrievedValue = (int)context; //??? not giving me the right number

}

but retrievedValue is giving me a number that has nothing to do to the original myValue…

How to retrieve that number?

thanks for any help.

Answer 1

See @DyingCactus‘s answer for how to get the integer.

OP’s code, however, has a serious problem on the context. Since the type of context is void*, UIKit will not expect you to pass an ObjC object into it, so the NSNumber will not be retained.

Therefore, when you perform

[(NSNumber*)context intValue];

in animationDidStop it’s almost certain that you’ll get some crazy numbers or crash.

There are 2 similar ways to solve this problem.

(a) Pass the object with retain count of +1, and release it in animationDidStop:

[UIView beginAnimations:nil context:[[NSNumber alloc] initWithInt:myValue]];
....
int retrievedValue = [(NSNumber*)context intValue];
[(NSNumber*)context release];

(b) Pass a malloc-ed memory, and free it in animationDidStop:

int* c = malloc(sizeof(*c));
*c = myValue;
[UIView beginAnimations:nil context:c];
....
int retrievedValue = *(int*)context;
free(context);