title: How can I dynamically adjust contentInset in scrollViewDidZoom? I initially set contentInset of UIImageView in UIScrollview
body: <p>I'm on a project that makes an custom <code>'Move and Scale' Controller</code> of <code>UIImagePickerController</code>. (controller when appear if <code>imagePickerController.allowsEditing=YES</code>)</p>
  
  <p>I want to <code>crop an UIImage</code> in the crop rectangular like the picture below.</p>
  
  <p><img src="https://i.stack.imgur.com/Cr3ux.png" alt="screenshot 1"> </p>
  
  <p>And I made some code to set <code>contentInset</code>.</p>
  
  <pre><code>    self.selectedImageView.backgroundColor = [UIColor redColor];
  
      CGRect cropRect = [SKPhotoCropFrameView getCropRectFromOrientation:self.photoCropOrientation];
      CGRect aspectFitRect = AVMakeRectWithAspectRatioInsideRect(self.selectedImageView.image.size, self.selectedImageView.frame);
      CGFloat difference = fabsf(cropRect.size.height - aspectFitRect.size.height);
      self.contentInset = UIEdgeInsetsMake(difference/2, 0, difference/2 + 20, 0);   // 20 is status bar height
  </code></pre>
  
  <p>and here is the result. </p>
  
  <p><img src="https://i.stack.imgur.com/Xp5SZ.png" alt="screenshot 2"></p>
  
  <p>Black region is contentInset area. </p>
  
  <p>However, if I pinch this scrollView to zoom in, something happen. </p>
  
  <p><img src="https://i.stack.imgur.com/P3Ghx.png" alt="screenshot 3"></p>
  
  <p>I think I have to do something on </p>
  
  <pre><code>    - (void)scrollViewDidZoom:(UIScrollView *)scrollView
  </code></pre>
  
  <p>to adjust contentInset dynamically. How can I do this? Please give me some help :)</p>