title: UIButtons not sticking to UIView edges
body: <p>Hi and thanks in advance. I'm attempting to bind two UIButtons to a <code>UIViewController</code>'s <code>view</code> like so:</p>
  
  <p>First by declaring them:</p>
  
  <pre><code>fileprivate var deleteButton: UIButton = UIButton(type: .system)
  fileprivate var addButton: UIButton = UIButton(type: .system)
  </code></pre>
  
  <p>Next in setting them up:</p>
  
  <pre><code>private func setupButtons() {
  
      deleteButton.setTitle("Delete", for: .normal)
      addButton.setTitle("Add", for: .normal)
  
      deleteButton.sizeToFit()
      addButton.sizeToFit()
  
      deleteButton.alpha = 1
      addButton.alpha = 1
  
      view.addSubview(deleteButton)
      view.addSubview(addButton)
  
      view.addConstraint(NSLayoutConstraint(item: deleteButton,
                                            attribute: .leading,
                                            relatedBy: .equal,
                                            toItem: view,
                                            attribute: .leading,
                                            multiplier: 1.0,
                                            constant: 0))
  
      view.addConstraint(NSLayoutConstraint(item: deleteButton,
                                            attribute: .bottom,
                                            relatedBy: .equal,
                                            toItem: view,
                                            attribute: .bottom,
                                            multiplier: 1.0,
                                            constant: 0))
  
      view.addConstraint(NSLayoutConstraint(item: addButton,
                                            attribute: .trailing,
                                            relatedBy: .equal,
                                            toItem: view,
                                            attribute: .trailing,
                                            multiplier: 1.0,
                                            constant: 0))
  
      view.addConstraint(NSLayoutConstraint(item: addButton,
                                            attribute: .bottom,
                                            relatedBy: .equal,
                                            toItem: view,
                                            attribute: .bottom,
                                            multiplier: 1.0,
                                            constant: 0))
  
  }
  </code></pre>
  
  <p>But running the simulator sticks the two UIButtons in the top left, the default CGRect frames assigned to them both.</p>
  
  <p>Might you know what i'm doing wrong? I feel like i'm close but perhaps it has something to do with re-drawing the view?</p>
  
  <p><a href="https://i.stack.imgur.com/7Zlwh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7Zlwh.png" alt="Halp!"></a></p>