title: iOS UITableViewCell selected background view cover image on cell issue
body: <p>I currently developing an iOS APP that has a table whose cell contains an image.
  And I set the selected background view to an UIBlurEffectView, when the cell is selected, its text labels can normally show up but the image does not.
  Here is the screenshot before selection:
  <img src="https://i.stack.imgur.com/STajk.png" alt="before selection"></p>
  
  <p>Here is the screenshot after selection:</p>
  
  <p><img src="https://i.stack.imgur.com/8qu7S.png" alt="after selection"></p>
  
  <p>Here is the codes setting the selected background view of cell:</p>
  
  <pre><code>let backgroundViewVisualEffectView = UIVisualEffectView(effect: UIBlurEffect(style: UIBlurEffectStyle.Light))
  backgroundViewVisualEffectView.frame = cell.bounds
  cell.selectedBackgroundView = backgroundViewVisualEffectView
  </code></pre>
  
  <p>Here is the codes adding the image to the cell:</p>
  
  <pre><code>let contentImageView = UIImageView()
  contentImageView.backgroundColor = UIColor.whiteColor()
  cell.contentView.addSubview(contentImageView)
  contentImageView.setTranslatesAutoresizingMaskIntoConstraints(false)
  cell.contentView.addConstraint(NSLayoutConstraint(item: contentImageView, attribute: .CenterY, relatedBy: .Equal, toItem: cell.contentView, attribute: .CenterY, multiplier: 1, constant: 0))
  cell.contentView.addConstraint(NSLayoutConstraint(item: contentImageView, attribute: .Trailing, relatedBy: .Equal, toItem: cell.contentView, attribute: .Trailing, multiplier: 1, constant: -cell.bounds.width/40))
  contentImageView.addConstraint(NSLayoutConstraint(item: contentImageView, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 0, constant: 1.5 * cell.bounds.height))
  contentImageView.addConstraint(NSLayoutConstraint(item: contentImageView, attribute: .Width, relatedBy: .Equal, toItem: contentImageView, attribute: .Height, multiplier: 1, constant: 0))
  </code></pre>
  
  <p>Why the image can not show up like text labels when I selecting the cell, any solutions?Thx</p>