如题，主要使用AsReadOnly这个方法就可以了
List<int> a = new List<int> {1, 2, 3, 4, 5};
IList<int> b = a.AsReadOnly(); // block modification...
IList<int> c = b.AsWritable(); // ... but unblock it again
c.Add(6);
Debug.Assert(a.Count == 6); // we've modified the original
IEnumerable<int> d = a.Select(x => x); // okay, try this...
IList<int> e = d.AsWritable(); // no, can still get round it
e.Add(7);