https://stackoverflow.com/questions/18080523/application-state-preservation-and-restoration-without-using-storyboard
http://www.apeth.com/iOSBook/ch19.html#_state_restoration
https://stackoverflow.com/questions/18080523/application-state-preservation-and-restoration-without-using-storyboard
http://www.apeth.com/iOSBook/ch19.html#_state_restoration