title: Set center point of UIView after CGAffineTransformMakeRotation
body: <p>I have a UIView that I want the user to be able to drag around the screen.</p>
  
  <pre><code>-(void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event 
  {
      CGPoint pt = [[touches anyObject] locationInView:self];
  
      CGPoint center = self.center;
  
      CGFloat adjustmentX = pt.x - startLocation.x;
      CGFloat adjustmentY = pt.y - startLocation.y;
  
     center.x += adjustmentX;
     center.y += adjustmentY;
  
     [self setCenter:center];
  }
  </code></pre>
  
  <p>works perfectly until I apply a transform to the view as follows:</p>
  
  <pre><code>self.transform = CGAffineTransformMakeRotation(....);
  </code></pre>
  
  <p>However, once the transform has been applied, dragging the UIView results in the view being moved in a exponential spiral effect.</p>
  
  <p>I'm assuming I have to make an correction for the rotation in the touchesMoved method, but so far all attempts have eluded me.</p>