Question

I would like to “detect” rotation – not to track it. I need to handle gesture rotation clockwise or counterclockwise by M_PI/8 and then should rotate my image by M_PI_2 or -M_PI_2.

Is it possible using UIRotationGestureRecognizer?

Answer 1

This code works as I need:

- (IBAction)rorationDid:(UIRotationGestureRecognizer *)recognizer
{
    static CGFloat angle = 0;
    if (recognizer.state == UIGestureRecognizerStateBegan)
        angle = recognizer.rotation;
    if (recognizer.state != UIGestureRecognizerStateEnded)
        return;

    float rotation = 0;
    if (angle - recognizer.rotation > M_PI/8)
        rotation = -M_PI_2;
    if (angle - recognizer.rotation < -M_PI/8)
        rotation = M_PI_2;

    if (rotation != 0.0)
    {
        // Let's do rotation
    }
}

UPDATE:

This code: static CGFloat angle = 0; should really be a @property not static.