CodingAutoLayout.swift

// iOS 9 or Above
// Reference: https://www.raywenderlich.com/125718/coding-auto-layout
//
avatarView.translatesAutoresizingMaskIntoConstraints = false
avatarView.topAnchor.constraintEqualToAnchor(topLayoutGuide.bottomAnchor).active = true
avatarView.leadingAnchor.constraintEqualToAnchor(view.layoutMarginsGuide.leadingAnchor).active = true
chapterLabel.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
avatarView.bottomAnchor.constraintEqualToAnchor(chapterLabel.topAnchor,constant: -10).active = true
chapterLabel.setContentHuggingPriority(UILayoutPriorityRequired, forAxis: .Vertical)
chapterLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, forAxis: .Vertical)

NSLayoutConstraint.activateConstraints([
      imageViewTop, imageViewBottom,
      labelBottom,
      socialMediaTrailing])
      
override func intrinsicContentSize() -> CGSize {
    return CGSize(width: UIViewNoIntrinsicMetric, height: 100)
  }
  
  override func traitCollectionDidChange(previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    
    if traitCollection.horizontalSizeClass == .Regular {
      NSLayoutConstraint.deactivateConstraints(compactConstraints)
      NSLayoutConstraint.activateConstraints(regularConstraints)
      socialMediaView.axis = .Horizontal
    } else {
      NSLayoutConstraint.deactivateConstraints(regularConstraints)
      NSLayoutConstraint.activateConstraints(compactConstraints)
      socialMediaView.axis = .Vertical
    }
  }
  
  override func updateConstraints() {
    super.updateConstraints()
    
    var aspectRatio: CGFloat = 1
    if let image = image {
      aspectRatio = image.size.width / image.size.height
    }
    
    aspectRatioConstraint?.active = false
    aspectRatioConstraint = imageView.widthAnchor.constraintEqualToAnchor(imageView.heightAnchor,multiplier: aspectRatio)
    aspectRatioConstraint?.active = true
  }
  
  override func layoutSubviews() {
    super.layoutSubviews()
    if bounds.height < socialMediaView.bounds.height {
      socialMediaView.alpha = 0
    } else {
      socialMediaView.alpha = 1
    }
    if imageView.bounds.height < 30 {
      imageView.alpha = 0
    } else {
      imageView.alpha = 1
    }
  }