Working with C# Anonymous Types

Question

I am calling a method that returns a List variable that contains a c# Anonymous Type objects. For example:

List<object> list = new List<object>(); foreach ( Contact c in allContacts ) {     list.Add( new {         ContactID = c.ContactID,         FullName = c.FullName     }); } return list; 

How do I reference this type properties in the code I am working on like for example

foreach ( object o in list ) {     Console.WriteLine( o.ContactID ); } 

I know that my sample is not possible, I have only wrote that way to say that I need to identify each property of the anonymous type exactly.

Thanks!

Solution:

Not just one of the answer is correct and/or suggest a working solution. I have ended up to using Option 3 of Greg answer. And I learned something very interesting regarding the dynamic in .NET 4.0!

Answer 1

You can't return a list of an anonymous type, it will have to be a list of object. Thus you will lose the type information.

Option 1
Don't use an anonymous type. If you are trying to use an anonymous type in more than one method, then create a real class.

Option 2
Don't downcast your anonymous type to object. (must be in one method)

var list = allContacts              .Select(c => new { c.ContactID, c.FullName })              .ToList();  foreach (var o in list) {     Console.WriteLine(o.ContactID); } 

Option 3
Use the dynamic keyword. (.NET 4 required)

foreach (dynamic o in list) {     Console.WriteLine(o.ContactID); } 

Option 4
Use some dirty reflection.

Answer 2

foreach ( var o in list ) {     Console.WriteLine( o.ContactID ); } 

this will work only if list is IEnumerable<anonymous type>, like this:

var list = allContacts.Select(c => new {         ContactID = c.ContactID,         FullName = c.FullName     }); } 

but you can't return anonymous types, because you must define return type (you can't return var) and anonymous types can't have names. you should create non-anonymous type if you with to pass it. Actually anonymous types should not be used too much, except for inside of queries.