title: CGAffineTransform to rotate UIButton
body: <p>I have a UIButton. On this button I apply a <code>CGAffineTransform</code> like this:</p>
  
  <pre><code>_mainButton.transform = CGAffineTransformMakeRotation((degrees-heading.trueHeading) * M_PI / 180);
  </code></pre>
  
  <p>In this way I can rotate all my buttons, but I would like to rotate only the background image. </p>
  
  <p>So, <code>myButton.imageView</code> should remain at its fixed location. How can make this?</p>