Rotating a wheel? - ios

Question

I have read here a few examples about that, but couldn't make it work.
I have some UIView called Wheel , in which i want to rotate while touch and drag.
It should work like a real wheel, so if i touch at some point it will NOT rotate to that point, only when i drag my finger, i will get rotation .
I tried this,but i get a full rotation for every little move i do. I would like to ADD the angel to the view, not ROTATE to the new angel ..
- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [[event allTouches] anyObject];
CGPoint touchPoint = [touch locationInView:self];
CGPoint center=wheel.center;
float xLeg = fabs(center.x - touchPoint.x);
float yLeg = fabs(center.y-touchPoint.y);
float angle = atan(xLeg / yLeg);
NSLog(#"%f",angle);
wheel.transform = CGAffineTransformMakeRotation( angleInDegree );
}

Answer 1

This should do the trick. Notice how I store the first touch point in touchesBegan:withEvent:. This allows me to subtract the first touch point from every touch point I get while dragging, and thus gives me the real angle I need to rotate.
EDIT
I've done some adjustments, so that it is now smooth and regular even after several touches.
Demo
WheelViewController.m
#interface WheelViewController () {
CGPoint startPoint;
CGFloat startAngle;
CGFloat endAngle;
}
#end
#implementation WheelViewController
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches] anyObject];
startPoint = [touch locationInView:self.view];
startAngle = [self angleForTouchPoint:startPoint] - endAngle;
NSLog(#"\r\nStart angle: %f", startAngle);
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [[event allTouches] anyObject];
CGPoint touchPoint = [touch locationInView:self.view];
CGFloat touchAngle = [self angleForTouchPoint:touchPoint];
NSLog(#"Touch angle: %f", touchAngle);
self.wheel.transform = CGAffineTransformMakeRotation(fmodf(touchAngle - startAngle, 2 * M_PI));
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches] anyObject];
CGPoint touchPoint = [touch locationInView:self.view];
endAngle = [self angleForTouchPoint:touchPoint] - startAngle;
NSLog(#"End angle: %f", endAngle);
}
- (CGFloat)angleForTouchPoint:(CGPoint)touchPoint {
CGPoint center = self.wheel.center;
float xLeg = touchPoint.x - center.x;
float yLeg = touchPoint.y - center.y;
float angle = fmodf(atan(yLeg/xLeg), (2 * M_PI));
if (xLeg < 0) {
angle += M_PI;
}
return angle;
}