问题
From what I can tell, .NET 4.0 still lacks read-only lists. Why does the framework still lack this functionality? Isn't this one of the commonest pieces of functionality for domain-driven design?
One of the few advantages Java has over C# is this in the form of the Collections.unmodifiablelist(list) method, which it seems is long overdue in IList<T> or List<T>.
Using IEnumerable<T> is the easiest solution to the question - ToList can be used and returns a copy.
回答1:
You're looking for ReadOnlyCollection, which has been around since .NET2.
IList<string> foo = ...;
// ...
ReadOnlyCollection<string> bar = new ReadOnlyCollection<string>(foo);
or
List<string> foo = ...;
// ...
ReadOnlyCollection<string> bar = foo.AsReadOnly();
This creates a read-only view, which reflects changes made to the wrapped collection.
回答2:
How about the ReadOnlyCollection already within the framework?
回答3:
For those who like to use interfaces:
.NET 4.5 adds the generic IReadOnlyList interface which is implemented by List<T> for example.
It is similar to IReadOnlyCollection and adds an Item indexer property.
回答4:
If the most common pattern of the list is to iterate through all the elements, IEnumerable<T> or IQueryable<T> can effectively act as a read-only list as well.
回答5:
In 2.0 you can call AsReadOnly to get a read-only version of the list. Or wrap an existing IList in a ReadOnlyCollection<T> object.
回答6:
What's wrong with System.Collections.ObjectModel.ReadOnlyCollection?
来源：https://stackoverflow.com/questions/984042/read-only-list-or-unmodifiable-list-in-net-4-0