Generating a list of child classes with reflection in .NET 3.5

Question

At runtime, I would like to specify a parent class, and then the program would generate a list of all children classes (of however many generations). For example, if I had

Answer 1

One possible way would utilize the Type.IsAssignableFrom method. You would loop over all types, and select those for which it is true.

Basically, it would be something like

Type parent = Type.GetType("Entity");
Type[] types = Assembly.GetExecutingAssembly().GetTypes(); // Maybe select some other assembly here, depending on what you need
Type[] inheritingTypes = types.Where(t => parent.IsAssignableFrom(t));

I don't have a compiler available at this time, so I can't verify it, but it should be mostly correct

Answer 2

This is what I use to find all children of some class (can be also abstract class) in selected assembly:

public class InheritedFinder
{
    public static Type[] FindInheritedTypes(
        Type parentType, Assembly assembly)
    {
        Type[] allTypes = assembly.GetTypes();
        ArrayList avTypesAL = new ArrayList();

        return allTypes.Where(
            t => parentType.IsAssignableFrom(t) && t != parentType).ToArray();
    }
}

Simply call by

var availableTypes = InheritedFinder.FindInheritedTypes(
        typeof(YourBaseClass),
        System.Reflection.Assembly.GetExecutingAssembly());

This will give you list of available children of YourBaseClass. Nice thing about it - it'll find also children of children, so you can use multi-level abstract classes. If you need to create instances of every child, easy:

var availableTypes= InheritedFinder.FindInheritedTypes(
    typeof(Shape), System.Reflection.Assembly.GetExecutingAssembly());
foreach (var t in availableTypes)
{
    try
    {
        YourBaseClass nInstance = (YourBaseClass)Activator.CreateInstance(t);
        //nInstance is now real instance of some children
    }
    catch (Exception e)
    {
        //recommended to keep here - it'll catch exception in case some class is abstract (=can't create its instance)
    }
}

Answer 3

var pType = typeof(Entity);
IEnumerable<string> children = Enumerable.Range(1, iterations)
   .SelectMany(i => Assembly.GetExecutingAssembly().GetTypes()
                    .Where(t => t.IsClass && t != pType
                            && pType.IsAssignableFrom(t))
                    .Select(t => t.Name));

Demo