How do I get the Array Item Type from Array Type in .net

Question

Say I have an System.String[] type object. I can query the type object to determine if it is an array

Type t1 = typeof(System.String[]); bool isAnArray = t1.IsArray; // should be true 

However how do I get a type object of the array item from t1

Type t2 = ....; // should be typeof(System.String) 

Answer 1

You can use the instance method Type.GetElementType for this purpose.

Type t2 = t1.GetElementType(); 

[Returns] the type of the object encompassed or referred to by the current array, pointer, or reference type, or null if the current Type is not an array or a pointer, or is not passed by reference, or represents a generic type or a type parameter in the definition of a generic type or generic method.

Answer 2

Thanks to @psaxton comment pointing out the difference between Array and other collections. As an extension method:

public static class TypeHelperExtensions {     /// <summary>     /// If the given <paramref name="type"/> is an array or some other collection     /// comprised of 0 or more instances of a "subtype", get that type     /// </summary>     /// <param name="type">the source type</param>     /// <returns></returns>     public static Type GetEnumeratedType(this Type type)     {         // provided by Array         var elType = type.GetElementType();         if (null != elType) return elType;          // otherwise provided by collection         var elTypes = type.GetGenericArguments();         if (elTypes.Length > 0) return elTypes[0];          // otherwise is not an 'enumerated' type         return null;     } } 

Usage:

typeof(Foo).GetEnumeratedType(); // null typeof(Foo[]).GetEnumeratedType(); // Foo typeof(List<Foo>).GetEnumeratedType(); // Foo typeof(ICollection<Foo>).GetEnumeratedType(); // Foo typeof(IEnumerable<Foo>).GetEnumeratedType(); // Foo  // some other oddities typeof(HashSet<Foo>).GetEnumeratedType(); // Foo typeof(Queue<Foo>).GetEnumeratedType(); // Foo typeof(Stack<Foo>).GetEnumeratedType(); // Foo typeof(Dictionary<int, Foo>).GetEnumeratedType(); // int typeof(Dictionary<Foo, int>).GetEnumeratedType(); // Foo, seems to work against key