title: How to automatically have content size increase in UIScrollView on an action with autolayout?
body: <p>I've setup a test project (<a href="https://github.com/coolbnjmn/LabelScrollViewTest" rel="nofollow">project here</a>)  for this question to better illustrate my question, but here is the core issue I'm facing:</p>
  
  <p>I have a <code>UILabel</code> nested within a content <code>UIView</code> which is itself nested inside a <code>UIScrollView</code>, and this is all laid out with AutoLayout. My initial layout works great, and the label is properly truncated to fit within it's content view as desired by the initial layout constraints. All is good so far.</p>
  
  <p>Now the issue is when I want to add an "expand" action on the label. Let's say any tap on the content view should expand the label such that there is no longer truncation, and instead of truncating inside the <code>contentView</code>'s bounds I want the <code>scrollView</code>'s <code>contentSize</code> to increase such that the full label's text can now be scrolled. How should I accomplish this?</p>
  
  <p>In the sample project, a tap on the content view will adjust the entire <code>scrollView</code>'s constraints just to illustrate that the label now has a different amount of space to work with. I'm stuck as to how to now have the <code>scrollView</code> recalculate it's <code>contentSize</code> such that the label no longer truncates. </p>
  
  <p>I've tried playing with content compression priority, and changing that based on the action being done, like so:     </p>
  
  <pre><code>theLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, forAxis: .Vertical)
  </code></pre>
  
  <p>But this doesn't seem to actually enforce that the label isn't going to truncate. I've also tried invalidating the intrinsic content size of the <code>scrollView</code> on the tap action, but to no avail. How do I toggle whether or not the label should truncate?</p>