title: Cocoa Custom Control not visible
body: <p>I try to define a Custom Control in Cocoa like this</p>
  
  <pre><code>@IBDesignable
  class MyCustomContol: NSControl
  { var textfield: NSTextField!
  
    required public init?(coder: NSCoder)
    { super.init(coder: coder)
  
      textfield = NSTextField(frame: self.frame)  
      textfield.backgroundColor = NSColor.yellow
      textfield.stringValue="DEFAULT"
      self.addSubview(textfield)
    }
  }  
  </code></pre>
  
  <p>In Interfacebuilder I added a Custom View and set its class to my class "MyCustomContol"</p>
  
  <p>The control does not appear in Interfacebuilder an not at runtime.</p>
  
  <p>What´s going wrong.</p>