Get all inherited classes of an abstract class

Question

I have an abstract class:

abstract class AbstractDataExport
{
        public string name;
        public abstract bool ExportData();
}

I have classes which are derived from AbstractDataExport:

class XmlExport : AbstractDataExport
{
    new public string name = "XmlExporter";
    public override bool ExportData()
    {
        ...
    }
}
class CsvExport : AbstractDataExport
{
    new public string name = "CsvExporter";
    public override bool ExportData()
    {
        ...
    }
}

Is it possible to do something like this? (Pseudocode:)

foreach (Implementation imp in Reflection.GetInheritedClasses(AbstractDataExport)
{
    AbstractDataExport derivedClass = Implementation.CallConstructor();
    Console.WriteLine(derivedClass.name)
}

with an output like

CsvExporter
XmlExporter

?

The idea behind this is to just create a new class which is derived from AbstractDataExport so i can iterate through all implementations automatically and add for example the names to a Dropdown-List. I just want to code the derived class without changing anything else in the project, recompile, bingo!

If you have alternative solutions: tell em.

Thanks

Answer 1

This is such a common problem, especially in GUI applications, that I'm surprised there isn't a BCL class to do this out of the box. Here's how I do it.

public static class ReflectiveEnumerator
{
    static ReflectiveEnumerator() { }

    public static IEnumerable<T> GetEnumerableOfType<T>(params object[] constructorArgs) where T : class, IComparable<T>
    {
        List<T> objects = new List<T>();
        foreach (Type type in 
            Assembly.GetAssembly(typeof(T)).GetTypes()
            .Where(myType => myType.IsClass && !myType.IsAbstract && myType.IsSubclassOf(typeof(T))))
        {
            objects.Add((T)Activator.CreateInstance(type, constructorArgs));
        }
        objects.Sort();
        return objects;
    }
}

A few notes:

• Don't worry about the "cost" of this operation - you're only going to be doing it once (hopefully) and even then it's not as slow as you'd think.
• You need to use Assembly.GetAssembly(typeof(T)) because your base class might be in a different assembly.
• You need to use the criteria type.IsClass and !type.IsAbstract because it'll throw an exception if you try to instantiate an interface or abstract class.
• I like forcing the enumerated classes to implement IComparable so that they can be sorted.
• Your child classes must have identical constructor signatures, otherwise it'll throw an exception. This typically isn't a problem for me.