Understanding CGAffineTransform interactions

Question

I'm trying to make a simple app where an image that is "pinned" ge's returned to its position after being moved by a finger. This is probably explained better with code:

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
     image.transform = CGAffineTransformIdentity;
}


- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    if (CGRectContainsPoint([image frame], [touch locationInView:nil])) 
    {
         image.center = [touch locationInView:nil];
    }
}

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
     if (pin) {
         CGPoint point = image.center;
         CGPoint center = self.view.center;
         //CGAffineTransform transform = CGAffineTransformMakeTranslation(0, 0);
         [UIView beginAnimations:nil context:NULL];
         [UIView setAnimationDuration:0.5];
         image.transform = CGAffineTransformMakeTranslation(center.x - point.x, center.y - point.y);
         //image.transform = CGAffineTransformConcat(image.transform, CGAffineTransformMakeTranslation(center.x - point.x, center.y - point.y));
    [UIView commitAnimations];

    }
}

Every time I press the image it shifts so that it moves out from under my finger. I think it has something to do with the transformations. Could anyone please point my in the right direction?

Answer 1

EDITED

I'd ACTUALLY do it like this:

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
}


- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    CGPoint location = [[touches anyObject] locationInView:[touch view]];
    CGPoint difference = CGPointMake(location.x - image.center.x, location.y - image.center.y);

    image.transform = CGAffineTransformTranslate(image.transform, difference.x, difference.y);
}

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    if (pin) {
        [UIView beginAnimations:nil context:NULL];
        [UIView setAnimationDuration:0.5];
        image.transform = CGAffineTransformIdentity;
        [UIView commitAnimations];
    }
}