System.Collections.ObjectModel

System.Collections.ObjectModel.ReadOnlyCollection

System.Collections.Generic.List <string> weekdays = new System.Collections.Generic.List <string>(); 

weekdays.Add("Monday"); 
weekdays.Add("Tuesday"); 
weekdays.Add("Wednesday"); 
weekdays.Add("Thursday"); 

ReadOnlyCollection<string> readOnlyWeekdays = new System.Collections.ObjectModel.ReadOnlyCollection<string>(weekdays);