title: Swift: Drag a UIView between two other UIViews
body: <p><img src="https://i.stack.imgur.com/mqlxX.png" alt="enter image description here">
  As seen in screenshot, I have two stationary green and red views side by side.
  Blue view is dragable.</p>
  
  <p>What I want is, when the blue view is dragged between green and red view, to move red and green views and make space for the blue view to be dropped. If blue view is dropped elsewhere, it is to return to its original position.</p>
  
  <p>I am able to drag the blue view, but not sure how to "Detect when the blue view is in between green and red and then drop it in place". Help in swift will be highly appreciated.</p>