title: How to get NSLayoutConstraint programmatically between UIButtons?
body: <p>In a view I'm inserting a new UIButton, As I have been using AutoLayout, I need to get constraint of the view below which I'm going to insert button. How do I get the NSLayoutConstraint programmatically, so that I can delete the old constraint create new one afterwards. Thanx.</p>
  
  <p>Edit:<img src="https://i.stack.imgur.com/7XZ0X.jpg" alt="enter image description here"></p>
  
  <p>with ref to diagram, I need to insert B3 between B1 and B2, So I need to delete the already set fixed space constraint between B1 and B2, and I need to connect B3 bottom to B2's top and B3's top to B1's bottom.</p>