According to the MSDN the, .AsReadOnly() method is listed as being supported by the PCL but I think it is not.
Can anyone verify this? If so are there any alternatives to make a collection as read only?
https://msdn.microsoft.com/en-us/library/e78dcd75(v=vs.100).aspx
https://developer.xamarin.com/api/member/System.Collections.Generic.List%3CT%3E.AsReadOnly()/