Why does Type.GetElementType return null?

I have a method that takes as an input parameter an object of type IEnumerable. I want to enumerate the enumeration and for each item use reflection to get the value for each property.

I have the following code:

protected void WriteData(IEnumerable data)
{
    var enumerationTypeInfo = data.GetType();
    var itemTypeInfo = enumerationTypeInfo.GetElementType();

    ...
}

The problem is enumerationTypeInfo.GetElementType() always returns null. In particular, I'm passing in a List<Entry> into WriteData, where开发者_运维技巧 Entry is a class I created. When I use the debugger and set a breakpoint I can see that enumerationTypeInfo correctly shows that it's a List of type Entry, but why does GetElementType return null?

Thanks

GetElementType() returns the element type of arrays. List<T> is not an array type, and therefore has no "element type."

If you want to get the type of elements a random IEnumerable<T> produces, try something like this:

public static Type GetEnumerableType(Type type)
{
    if (type == null)
        throw new ArgumentNullException("type");

    if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(IEnumerable<>))
        return type.GetGenericArguments()[0];

    var iface = (from i in type.GetInterfaces()
                 where i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IEnumerable<>)
                 select i).FirstOrDefault();

    if (iface == null)
        throw new ArgumentException("Does not represent an enumerable type.", "type");

    return GetEnumerableType(iface);
}

Note that types can implement more than one version of the same generic interface; a type can implement both IEnumerable<int> and IEnumerable<string> for example. How you handle that case is up to you. The method I provide will take whichever interface type the runtime hands it first.

See an example using the above method on ideone.

GetElementType is for use with arrays, not other generic classes. To get a generic type's generic parameters, you can use Type.GetGenericArguments.