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 i         


        

Answer 1

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

public static class TypeHelperExtensions
{
    /// 

    /// If the given  is an array or some other collection
    /// comprised of 0 or more instances of a "subtype", get that type
    /// 
    /// the source type
    /// 
    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).GetEnumeratedType(); // Foo
typeof(ICollection).GetEnumeratedType(); // Foo
typeof(IEnumerable).GetEnumeratedType(); // Foo

// some other oddities
typeof(HashSet).GetEnumeratedType(); // Foo
typeof(Queue).GetEnumeratedType(); // Foo
typeof(Stack).GetEnumeratedType(); // Foo
typeof(Dictionary).GetEnumeratedType(); // int
typeof(Dictionary).GetEnumeratedType(); // Foo, seems to work against key