title: UIAppearance Swift 4
body: <p>After updating to Swift 4, I am getting a compiler error: </p>
  
  <p><code>Static member 'appearance' cannot be used on protocol metatype 'UIAppearance.Protocol'</code></p>
  
  <p>Here is my <code>viewWillAppear</code> method in my custom Tab Bar Controller subclass, I am setting the font of the item text.</p>
  
  <pre><code>override func viewWillAppear(_ animated: Bool) {
      super.viewWillAppear(animated)
  
      // compiler error on line below
      UIAppearance.appearance().setTitleTextAttributes([NSAttributedStringKey.font: font], for: UIControlState.normal)
  }
  </code></pre>
  
  <p>I'm having trouble fixing this, any guidance would be appreciated, thanks!</p>