Question

Hi I have a UIImageView which is part on, part off screen.

I want to rotate the view around a point off screen (the center of the view.)

How do I do this?

fullRotationAnimation           = [CABasicAnimation animationWithKeyPath:@"transform.rotation"];
    fullRotationAnimation.fromValue= [NSNumber numberWithFloat:0.0f];
    fullRotationAnimation.toValue   = [NSNumber numberWithFloat:2 * M_PI];
    fullRotationAnimation.duration  = 4;
    fullRotationAnimation.repeatCount = 1;
    [self->greyRings.layer addAnimation:fullRotationAnimation forKey:@"360"];

I’m using that code at the moment but it just spins it around the center of the screen.

Any ideas please?

Answer 1

Using block animation:

- (void)rotateImageView:(UIImageView *)imageView aroundPoint:(CGPoint)point byAngle:(CGFloat)angle {

    CGFloat sinA = sin(angle);
    CGFloat cosA = cos(angle);
    CGFloat x = point.x;
    CGFloat y = point.y;

    CGAffineTransform transform = CGAffineTransformMake(cosA,sinA,-sinA,cosA,x-x*cosA+y*sinA,y-x*sinA-y*cosA);

    [UIView animateWithDuration:4.0 animations:^{
        imageView.transform = transform;
    }];
}

Note that angle is in radians, so a full rotation is 2.0*M_PI.