Determine if object derives from collection type

Question

I want to determine if a generic object type (\"T\") method type parameter is a collection type. I would typically be sending T through as a Generic.List but it could be any co

Answer 1

Personally I tend to use a method that I wrote myself, called TryGetInterfaceGenericParameters, which I posted below. Here is how to use it in your case:

Example of use

object currentObj = ...;  // get the object
Type[] typeArguments;
if (currentObj.GetType().TryGetInterfaceGenericParameters(typeof(IEnumerable<>), out typeArguments))
{
    var innerType = typeArguments[0];
    // currentObj implements IEnumerable
}
else
{
    // The type does not implement IEnumerable for any T
}

It is important to note here that you pass in typeof(IEnumerable<>), not typeof(IEnumerable) (which is an entirely different type) and also not typeof(IEnumerable) for any T (if you already know the T, you don’t need this method). Of course this works with any generic interface, e.g. you can use typeof(IDictionary<,>) as well (but not typeof(IDictionary)).

Method source

/// 

///     Determines whether the current type is or implements the specified generic interface, and determines that
///     interface's generic type parameters.
/// 
///     The current type.
/// 
///     A generic type definition for an interface, e.g. typeof(ICollection<>) or typeof(IDictionary<,>).
/// 
///     Will receive an array containing the generic type parameters of the interface.
/// 
///     True if the current type is or implements the specified generic interface.
public static bool TryGetInterfaceGenericParameters(this Type type, Type @interface, out Type[] typeParameters)
{
    typeParameters = null;

    if (type.IsGenericType && type.GetGenericTypeDefinition() == @interface)
    {
        typeParameters = type.GetGenericArguments();
        return true;
    }

    var implements = type.FindInterfaces((ty, obj) => ty.IsGenericType && ty.GetGenericTypeDefinition() == @interface, null).FirstOrDefault();
    if (implements == null)
        return false;

    typeParameters = implements.GetGenericArguments();
    return true;
}