the method of realizing one finger rotation

gestureSubclass.md

onefingerRotationGesture

pangesture.m

@interface RotationView()
@property (nonatomic, strong, readonly) UILabel *rotationView;
@property (nonatomic, strong, readonly) UIPanGestureRecognizer *pan;

@property (nonatomic, assign) CGPoint previousPoint;
@property (nonatomic, assign) CGPoint currentPoint;
@end

_rotationView.userInteractionEnabled = YES;
_pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
[_rotationView addGestureRecognizer:_pan];
    
- (void)rotation{
  CGRect rect = self.rotationView.frame;
  CGPoint centerPt = CGPointMake(CGRectGetMidX(rect), CGRectGetMidY(rect));
  
  float prevAngle = atan2f(self.previousPoint.y - centerPt.y, self.previousPoint.x - centerPt.x);
  float currAngle = atan2f(self.currentPoint.y - centerPt.y, self.currentPoint.x - centerPt.x);
  
  float deltaAngle = currAngle - prevAngle;

  NSLog(@"pan-- curr:%.2f, prev:%.2f, delta:%.2f", currAngle, prevAngle, deltaAngle);
  self.rotationView.transform = CGAffineTransformRotate(self.rotationView.transform, deltaAngle);
}

- (void)pan:(UIPanGestureRecognizer *)pan{
  CGPoint pt = [pan locationInView:self];
    switch (pan.state) {
    case UIGestureRecognizerStateBegan:
      self.previousPoint = pt;
      break;
    case UIGestureRecognizerStateChanged:
      self.currentPoint = pt;
      [self rotation];
      self.previousPoint = self.currentPoint;
      break;
      
    case UIGestureRecognizerStatePossible: break;
    case UIGestureRecognizerStateEnded: break;
    case UIGestureRecognizerStateCancelled: break;
    case UIGestureRecognizerStateFailed: break;
  }
  
  [pan setTranslation:CGPointZero inView:self];
}

usetouchEvents.m

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
  CGPoint prevPt = [touches.anyObject previousLocationInView:self];
  CGPoint currPt = [touches.anyObject locationInView:self];
  
  CGPoint centerPt = self.rotationV.frame.origin;
  
  float prevAngle = atan2f(prevPt.y - centerPt.y, prevPt.x - centerPt.x);
  float currAngle = atan2f(currPt.y - centerPt.y, currPt.x - centerPt.x);
  
  float deltaAngle = currAngle - prevAngle;
  
  self.rotationV.transform = CGAffineTransformRotate(self.rotationV.transform, deltaAngle);
}