CODEWITHSUNDEEP
c#reflection
weilin8
weilin8

Reputation: 2985

Find all derived types of generic class

I have a generic class and a derived class as following. 

public class GenericClass<T> { ... }

public class DerivedClass : GenericClass<SomeType> { ... }

How do I find the derived class via reflection? I have tried both ways below, but doesn't seem to work. 

System.Reflection.Assembly.GetExecutingAssembly().GetTypes().Where(t => typeof(GenericClass<>).IsAssignableFrom(t));

System.Reflection.Assembly.GetExecutingAssembly().GetTypes().Where(t => t.IsSubclassOf(typeof(GenericClass<>));

Upvotes: 25

Views: 10267

Answers (4)

Pavel Vladov
Pavel Vladov

Reputation: 4837

It's a bit more complex than that. t.BaseType may return null (e.g. when t is an interface). Also note that the Type.IsSubclassOf method does not work for generic types! If you are dealing with a generic type you should use the GetTypeDefinition method. I recently blogged about how to get all derived types of a class. Here's an IsSubclass method that works for generics, too:

public static bool IsSubclassOf(Type type, Type baseType)
{
    if (type == null || baseType == null || type == baseType)
        return false;

    if (baseType.IsGenericType == false)
    {
        if (type.IsGenericType == false)
            return type.IsSubclassOf(baseType);
    }
    else
    {
        baseType = baseType.GetGenericTypeDefinition();
    }

    type = type.BaseType;
    Type objectType = typeof(object);
    while (type != objectType && type != null)
    {
        Type currentType = type.IsGenericType
            ? type.GetGenericTypeDefinition()
            : type;
        if (currentType == baseType)
            return true;

        type = type.BaseType;
     }

    return false;
}

Upvotes: 12

Cosmin
Cosmin

Reputation: 2385

An improved (shorter) version of Kim's answer:

    public List<Type> GetAllDerivedTypes(Type baseType)
    {
        Assembly assembly = Assembly.LoadFrom(baseType.Assembly.Location);
        Type[] typesInAssembly = assembly.GetTypes();

        var results = new List<Type>();
        GetAllDerivedTypesRecursively(typesInAssembly, baseType, ref results);

        return results;
    }

    private static void GetAllDerivedTypesRecursively(Type[] types, Type baseType, ref List<Type> results)
    {
        Type[] derivedTypes;

        if (baseType.IsGenericType)
            derivedTypes = types.Where(t => t.BaseType != null && t.BaseType.IsGenericType && t.BaseType.GetGenericTypeDefinition() == baseType).ToArray();
        else
            derivedTypes = types.Where(t => t != baseType && baseType.IsAssignableFrom(t)).ToArray();

        results.AddRange(derivedTypes);

        foreach (Type derivedType in derivedTypes)
            GetAllDerivedTypesRecursively(types, derivedType, ref results);
    }

Upvotes: 0

Kim
Kim

Reputation: 1118

Because I needed to recursively find all derived types I wrote this code and will share with anyone who may need it:

    public void ListAllDerviedTypes()
    {
        Type entityType = typeof(TableAdapter);
        Assembly assembly = Assembly.LoadFrom(entityType.Assembly.Location);
        Type[] types = assembly.GetTypes();

        List<Type> results = new List<Type>();
        GetAllDerivedTypesRecursively(types, typeof(SiteAndSectorsTable<>), ref results);

        foreach (var type in results)
        {
            Console.WriteLine(type.Name);
        }
    }

    private static void GetAllDerivedTypesRecursively(Type[] types, Type type1, ref List<Type> results)
    {
        if (type1.IsGenericType)
        {
            GetDerivedFromGeneric(types, type1, ref results);
        }
        else
        {
            GetDerivedFromNonGeneric(types, type1, ref results);
        }
    }

    private static void GetDerivedFromGeneric(Type[] types, Type type, ref List<Type> results)
    {
        var derivedTypes = types
            .Where(t => t.BaseType != null && t.BaseType.IsGenericType &&
                        t.BaseType.GetGenericTypeDefinition() == type).ToList();
        results.AddRange(derivedTypes);
        foreach (Type derivedType in derivedTypes)
        {
            GetAllDerivedTypesRecursively(types, derivedType, ref results);
        }
    }


    public static void GetDerivedFromNonGeneric(Type[] types, Type type, ref List<Type> results)
    {
        var derivedTypes = types.Where(t => t != type && type.IsAssignableFrom(t)).ToList();

        results.AddRange(derivedTypes);
        foreach (Type derivedType in derivedTypes)
        {
            GetAllDerivedTypesRecursively(types, derivedType, ref results);
        }
    }

Upvotes: 2

Hans Passant
Hans Passant

Reputation: 942247

var result = System.Reflection.Assembly.GetExecutingAssembly()
    .GetTypes()
    .Where(t => t.BaseType != null && t.BaseType.IsGenericType && 
                t.BaseType.GetGenericTypeDefinition() == typeof(GenericClass<>));

Upvotes: 49

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