Get all types implementing specific open generic type

Question

How do I get all types that implementing a specific open generic type?

For instance:

public interface IUserRepository : IRepository<User>

Find all types that implement IRepository<>.

public static IEnumerable<Type> GetAllTypesImplementingOpenGenericType(Type openGenericType, Assembly assembly)
{
  ...
}

Baudelaire

Answer 1

This will return all types that inherit a generic base class. Not all types that inherit a generic interface.

var AllTypesOfIRepository = from x in Assembly.GetAssembly(typeof(AnyTypeInTargetAssembly)).GetTypes()
 let y = x.BaseType
 where !x.IsAbstract && !x.IsInterface &&
 y != null && y.IsGenericType &&
 y.GetGenericTypeDefinition() == typeof(IRepository<>)
 select x;

This will return all types, including interfaces, abstracts, and concrete types that have the open generic type in its inheritance chain.

public static IEnumerable<Type> GetAllTypesImplementingOpenGenericType(Type openGenericType, Assembly assembly)
{
    return from x in assembly.GetTypes()
            from z in x.GetInterfaces()
            let y = x.BaseType
            where
            (y != null && y.IsGenericType &&
            openGenericType.IsAssignableFrom(y.GetGenericTypeDefinition())) ||
            (z.IsGenericType &&
            openGenericType.IsAssignableFrom(z.GetGenericTypeDefinition()))
            select x;
}

This second method will find ConcreteUserRepo and IUserRepository in this example:

public class ConcreteUserRepo : IUserRepository
{}

public interface IUserRepository : IRepository<User>
{}

public interface IRepository<User>
{}

public class User
{}

Plataea

Yes, but you will only get the concreterepo and irepo when it is in the same assembly. But this is absolutely ok. – Baudelaire

Good catch! We'd have to be careful to load all the dependent assemblies, not just scan the currently loaded. Here's a SO about loading all assemblies: #2385092 – Plataea

The typeof(IRepository<>) works only if the generic type has a single generic parameter. Any ideas for types that have more than one generic type parameter? – Streit

Sorry, I found the answer. All you have to do is typeof(IRepository<,>) (assuming two generic type parameters) and so on! Cool! – Streit

Won't this only work when the concrete type directly inherits the interface being searched for? – Galliard

Answer 2

Solution implemented without LINQ, searching both generic and non generic interfaces, filtering the return type to classes.

public static class SampleCode
{
    public static void Main()
    {
        IList<Type> loadableTypes;

        // instance the dummy class used to find the current assembly
        DummyClass dc = new DummyClass();

        loadableTypes = GetClassesImplementingAnInterface(dc.GetType().Assembly, typeof(IMsgXX)).Item2;
        foreach (var item in loadableTypes) {Console.WriteLine("1: " + item);}
        // print
        // 1: Start2.MessageHandlerXY

        loadableTypes = GetClassesImplementingAnInterface(dc.GetType().Assembly, typeof(IHandleMessageG<>)).Item2;
        foreach (var item in loadableTypes) { Console.WriteLine("2: " + item); }
        // print
        // 2: Start2.MessageHandlerXY
        // 2: Start2.MessageHandlerZZ
    }

    ///<summary>Read all classes in an assembly that implement an interface (generic, or not generic)</summary>
    //
    // some references
    // return all types implementing an interface
    // https://mcmap.net/q/63745/-getting-all-types-that-implement-an-interface/12602220#12602220
    // http://haacked.com/archive/2012/07/23/get-all-types-in-an-assembly.aspx/
    // https://mcmap.net/q/64886/-how-to-prevent-reflectiontypeloadexception-when-calling-assembly-gettypes
    // return all types implementing a generic interface
    // https://mcmap.net/q/245044/-find-all-types-implementing-a-certain-generic-interface-with-specific-t-type
    // https://mcmap.net/q/243775/-get-all-types-implementing-specific-open-generic-type
    // https://mcmap.net/q/245045/-finding-out-if-a-type-implements-a-generic-interface
    // https://mcmap.net/q/245046/-net-getting-all-implementations-of-a-generic-interface
    public static Tuple<bool, IList<Type>> GetClassesImplementingAnInterface(Assembly assemblyToScan, Type implementedInterface)
    {
        if (assemblyToScan == null)
            return Tuple.Create(false, (IList<Type>)null);

        if (implementedInterface == null || !implementedInterface.IsInterface)
            return Tuple.Create(false, (IList<Type>)null);

        IEnumerable<Type> typesInTheAssembly;

        try
        {
            typesInTheAssembly = assemblyToScan.GetTypes();
        }
        catch (ReflectionTypeLoadException e)
        {
            typesInTheAssembly = e.Types.Where(t => t != null);
        }

        IList<Type> classesImplementingInterface = new List<Type>();

        // if the interface is a generic interface
        if (implementedInterface.IsGenericType)
        {
            foreach (var typeInTheAssembly in typesInTheAssembly)
            {
                if (typeInTheAssembly.IsClass)
                {
                    var typeInterfaces = typeInTheAssembly.GetInterfaces();
                    foreach (var typeInterface in typeInterfaces)
                    {
                        if (typeInterface.IsGenericType)
                        {
                            var typeGenericInterface = typeInterface.GetGenericTypeDefinition();
                            var implementedGenericInterface = implementedInterface.GetGenericTypeDefinition();

                            if (typeGenericInterface == implementedGenericInterface)
                            {
                                classesImplementingInterface.Add(typeInTheAssembly);
                            }
                        }
                    }
                }
            }
        }
        else
        {
            foreach (var typeInTheAssembly in typesInTheAssembly)
            {
                if (typeInTheAssembly.IsClass)
                {
                    // if the interface is a non-generic interface
                    if (implementedInterface.IsAssignableFrom(typeInTheAssembly))
                    {
                        classesImplementingInterface.Add(typeInTheAssembly);
                    }
                }
            }
        }
        return Tuple.Create(true, classesImplementingInterface);
    }
}

public class DummyClass
{
}

public interface IHandleMessageG<T>
{
}

public interface IHandleMessage
{
}

public interface IMsgXX
{
}

public interface IMsgXY
{
}

public interface IMsgZZ
{
}

public class MessageHandlerXY : IHandleMessageG<IMsgXY>, IHandleMessage, IMsgXX
{
    public string Handle(string a)
    {
        return "aaa";
    }
}

public class MessageHandlerZZ : IHandleMessageG<IMsgZZ>, IHandleMessage
{
    public string Handle(string a)
    {
        return "bbb";
    }
}

Consuela

awesome job. works in dotnet 2.2. just suggest changing assemblyToScan from single to an array of params params Assembly[] assemblies – Eada

Answer 3

You could try

openGenericType.IsAssignableFrom(myType.GetGenericTypeDefinition()) 

or

myType.GetInterfaces().Any(i => i.GetGenericTypeDefinition() = openGenericType)

Esmaria

Answer 4

You can use the following code to get all types that implement IRepository<> interface:

List<Type> typesImplementingIRepository = new List<Type>();
IEnumerable<Type> allTypesInThisAssembly = Assembly.GetExecutingAssembly().GetTypes();

foreach (Type type in allTypesInThisAssembly)
{
    if (type.GetInterface(typeof(IRepository<>).Name.ToString()) != null)
    {
        typesImplementingIRepository.Add(type);
    }
}

Presumptuous