title: Need a completion block for SnapKit constraints in a UIView
body: <p>I have a UIView in swift using SnapKit to layout it's views. I want to blur one of the views, but I need to put the blur code in a method that runs AFTER all the layout code is finished and that one view has it's proper size.</p>
  
  <p>I can't seem to figure out the right place for that blur code to go. Since snapkit is all based on blocks, it's all asynchronous and I don't know when it will be finished. What callback method can I use?</p>
  
  <p>EDIT: I reported an <a href="https://github.com/SnapKit/SnapKit/issues/187" rel="nofollow">issue on SnapKit</a> and they say the blocks are synchronous after all. However, in <code>layoutSubviews</code> (and after the synchronous blocks) my frames are all still <code>CGRectZero</code>, so the blur code can't snapshot and blur a view of 0 width or height.</p>