What is  NSUserDefault? How to use NSUserDefault in Xamarin.IOS?
Sometimes a developer has a requirement to store some basic user data dealing with user settings and app configuration. There are plenty of ways that Xamarin.iOS provides to save this data in your app. One such way is through NSUserDefaults. The NSUserDefaults class is very much like plist in the sense it stores key-value pairs. It is not recommended storing anything with sensitive user information (username, password, etc) as these values are saved in a plain text .plist file in the documents directory. To read from or write to NSUserDefaults, one has to get a reference to it.  In the simplest use of NSUserDefaults, this is done via a method that returns a reference to an object capable of interacting with NSUserDefaults's data store.