UIImageView how to track clockwise or counterclockwise user motion - iphone

Question

I have successfully implemented rotating a uiimageview using this code from this post
iPhone - Wheel tracking finger jumps to same starting position?
My question to fellow developers is that the user on touch can rotate the image both clockwise and counterclockwise. Is there a way I can detect in which direction is the user moving the view?
Its important to me because I am making a clock app. I let users move the min hand form 0 min all the way to 60 min. When it reaches there I move the hour hand one up. But the user can spin the min hand counter clockwise in which case I need to move the hour hand one down. Any ideas?

Answer 1

you can set a member variable named "lastPoint" to record the point last time you moved
the you can calc the direction next time
CGPoint lastPoint;
- (void) touchedBegin:(NSSet *)touches withEvent:(UIEvent *)event {
lastPoint = [touch locationInView:self.view];
}
-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
NSSet *allTouches = [event allTouches];
//you can save the point , then used in next time you want
int tInput = [allTouches count]-1;
UITouch *touch =[[allTouches allObjects] objectAtIndex:tInput];
CGPoint location = [touch locationInView:self.view];
float theAngle = atan2( location.y-imageX.center.y, location.x-imageX.center.x );
float theLastAngle = atan2( lastPoint.y-imageX.center.y, lastPoint.x-imageX.center.x );
lastPoint = location;
// compare theAngle & theLastAngle , so you can know it is clockwise or counterclockwise.
}