title: How to set constraints from the bottom of a collectionView to the top of Input Accessory View in Swift 4
body: <p>so I am having a bit of a trouble getting one of my constraints right.Basically I am using storyboard to put two views on the screen. One is a UITextView and the other is a collectionView. CollectionView is underneath UItextView. I want my collectionView's bottom constraint to be connected to the top of my Input Accessory View which pops up everytime keyboard appears. 
  By doing this I am essentially making the textview height dynamic. Is there any way I can do this?
  <a href="https://i.stack.imgur.com/bg0ey.png" rel="nofollow noreferrer">Here is a picture</a>
   The two circles are part of Input Accessory View. I want the collectionview which is the priority levels to be connected to the top of the input accessory view. 
  Here is another picture with detailed labeling and markup:
  <a href="https://i.stack.imgur.com/vLztP.png" rel="nofollow noreferrer">Detailed markup</a>
  Please help! </p>