Variable-height UILabel with auto layout in RubyMotion In response to: http://stackoverflow.com/questions/17959964/uilabel-dynamic-height-within-uitableviewcell-acts-erratic

event_cell.rb

class EventCell < UITableViewCell
  IDENTIFIER   = 'EventCell'
  PADDING      = 10
  LEFT_MARGIN  = 40
  RIGHT_MARGIN = 20

  attr_reader :event

  def initWithStyle(style, reuseIdentifier: reuse_identifier)
    super.tap do |cell|
      cell.contentView.addSubview(title)
      cell.contentView.addSubview(location)

      cell.setup_constraints
    end
  end

  def event=(event)
    @event = event

    title.text    = event[:title]
    location.text = event[:location]
  end

  def setup_constraints
    ['H:|-left_margin-[title]-right_margin-|',
     'H:|-left_margin-[location]-right_margin-|',
     'V:|[title]-padding-[location]'].each do |visual_format|
      contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat(
        visual_format,
        options: 0,
        metrics: metrics,
        views: subviews_dict))
    end
  end

  def metrics
    { 'left_margin'  => LEFT_MARGIN,
      'right_margin' => RIGHT_MARGIN,
      'padding'      => PADDING }
  end

  def subviews_dict
    { 'title'    => title,
      'location' => location }
  end

  def intrinsicContentSize
    content_height = labels.inject(0) {|sum, label| sum + label.intrinsicContentSize.height }

    CGSizeMake(-1, content_height + PADDING)
  end

  def labels
    [title, location]
  end

  def title
    @title ||= build_label.tap do |label|
      label.font = UIFont.fontWithName('Helvetica', size: 36.0)
    end
  end

  def location
    @location ||= build_label.tap do |label|
      label.font = UIFont.fontWithName('Helvetica', size: 16.0)
    end
  end

  def build_label
    UILabel.alloc.init.tap do |label|
      label.lineBreakMode = NSLineBreakByWordWrapping
      label.numberOfLines = 0
      label.setPreferredMaxLayoutWidth(contentView.size.width - (LEFT_MARGIN + RIGHT_MARGIN))
      label.translatesAutoresizingMaskIntoConstraints = false
    end
  end
end

events_controller.rb

class EventsController < UITableViewController
  def viewDidLoad
    super

    register_cells

    tableView.dataSource = self
    tableView.delegate   = self
  end

  def register_cells
    tableView.registerClass(EventCell, forCellReuseIdentifier: EventCell::IDENTIFIER)
  end

  def tableView(table_view, numberOfRowsInSection: section)
    events.count
  end

  def tableView(table_view, cellForRowAtIndexPath: index_path)
    table_view.dequeueReusableCellWithIdentifier(EventCell::IDENTIFIER).tap do |cell|
      event = events[index_path.row]

      cell.event = event
    end
  end

  def tableView(table_view, heightForRowAtIndexPath: index_path)
    cell = table_view.dataSource.tableView(table_view, cellForRowAtIndexPath: index_path)

    cell.intrinsicContentSize.height
  end
  
  def events
    [{ title: "Flashlight Tour on a 'Haunted' Aircraft Carrier",
       location: 'USS Hornet Museum' },
     { title: 'Dinner and a Movie',
       location: 'Grant Park' }]
  end
end