animationDuration problem

C4Workspace.m

//
//  C4WorkSpace.m
//  Examples
//
//  Created by Greg Debicki.
//

#import "C4WorkSpace.h"

@implementation C4WorkSpace {
    C4Shape *s1;
}

-(void)setup {
    [self setupShapes];
}

-(void) setupShapes {
    
    CGRect rect = CGRectMake(0, 0, 100, 100);
    
    s1 = [C4Shape ellipse:rect];
    
    CGPoint currentCenter = self.canvas.center;
    s1.center = currentCenter;

    [self.canvas addShape:s1];
    s1.alpha = 0.0f;
    s1.userInteractionEnabled = NO;
    
    

}

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    
    CGPoint touchedPoint = [[touches anyObject] locationInView:self.view];
    s1.animationDuration = 0.0f;
    s1.center = touchedPoint;
    s1.alpha = 1.0f;
    s1.animationDuration = 1.0f;
    s1.alpha = 0.0f;
    
}

@end