title: How to migrate SharedPreferences during update?
body: <p>I would like to change a SharedPreference from Boolean to String. The default value was true and will be "enabled". This is not a problem because it will be set automatically. But how can I check if it was set to false and then set the new preferece to "disabled"? Is there a method called during update of the app where I could migrate this preference?
  If I don't migrate it, the state of this preference is lost during update...</p>