title: Get height of uiview added by autolayout
body: <p>I am added a view in viewDidAppear method using autolayout. In the end of viewDidAppear trying to find the height of view that I added , I am getting zero? </p>
  
  <p>That view I am adding has a label , height of that label is dynamic</p>
  
  <pre><code>let viewToShowIn = self.view!
  let bannerView = UIView()
  bannerView.backgroundColor = UIColor.red
  
  let label = UILabel()
  label.translatesAutoresizingMaskIntoConstraints = false
  
  viewToShowIn.addSubview(bannerView)
  bannerView.addSubview(label)
  
  let margins = viewToShowIn.layoutMarginsGuide
  
  bannerView.translatesAutoresizingMaskIntoConstraints = false
  
  bannerView.leadingAnchor.constraint(equalTo: viewToShowIn.leadingAnchor, constant: 0).isActive = true
  bannerView.trailingAnchor.constraint(equalTo: viewToShowIn.trailingAnchor, constant: 0).isActive = true
  let bannerTopConstraint =    bannerView.topAnchor.constraint(equalTo: margins.topAnchor, constant: 0)
  bannerTopConstraint.isActive = true
  
  label.font = UIFont.systemFont(ofSize: 20)
  label.text = "kjafj kfj fk fjk dakjd k fdjakljf dkfjklsdjf dfsjlkj lkfsdjlkjl sjflksdjfljslf sdfljdslkjflsdjf sldfjlksj"
  label.numberOfLines = 0
  label.lineBreakMode = .byWordWrapping
  label.textAlignment = .center
  
  label.leadingAnchor.constraint(equalTo: bannerView.leadingAnchor, constant: 20).isActive = true
  label.trailingAnchor.constraint(equalTo: bannerView.trailingAnchor, constant: -20).isActive = true
  label.topAnchor.constraint(equalTo: bannerView.topAnchor, constant: 10).isActive = true
  bannerView.bottomAnchor.constraint(equalTo: label.bottomAnchor, constant: 10).isActive = true
  </code></pre>