UIScrollView与其他手势共存

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer 
shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {  
  if (self.contentOffset.x <= 0) { 
       return YES; 
   }    
  return NO;
}