how to stop animation after using beginAnimations?

Question

i use the following code to do a string rolling, but how to stop the animation?

[UIView beginAnimations:@"ruucc" context:NULL];
[UIView setAnimationDuration:12.8f];  
[UIView setAnimationCurve:UIViewAnimationCurveLinear];  
[UIView setAnimationDelegate:self];  
[UIView setAnimationRepeatAutoreverses:NO];  
[UIView setAnimationRepeatCount:999999]; 

frame = label1.frame;
frame.origin.x = -12;
label1.frame = frame;
[UIView commitAnimations];