title: How to show/hide button with switch that saves value in NSUserDefaults
body: <p>I have <strong>UISwitch</strong> named <strong>sosSwitch</strong> thas saves value in <strong>NSUserDefaults</strong> key: <strong>MySwitch</strong> and I have <strong>UIButton</strong> named <strong>sosBtn</strong>.
  How can I show/hide <strong>sosBtn</strong> depending on the switch value that was saved in <strong>NSUserDefaults</strong>? And where I need to put the code? In viewDidLoad? Thank you!</p>