Dynamically create type and call constructor of base-class

Question

I need to create a class dynamically. Most things work fine but i'm stuck in generating the constructor.

AssemblyBuilder _assemblyBuilder =
        AppDomain.CurrentDomain.DefineDynamicAssembly(new AssemblyName("MyBuilder"),                                                        AssemblyBuilderAccess.Run);

ModuleBuilder _moduleBuilder = _assemblyBuilder.DefineDynamicModule("MyModule");

public static object GetInstance<TSource, TEventArgs>(this TSource source, string eventName)
    where TSource : class
{
    var typeName = "MyTypeName";
    var typeBuilder = _moduleBuilder.DefineType(typeName, TypeAttributes.Class | TypeAttributes.Public);

    // create type like class MyClass : GenericType<MyClass, TSource, TEventArgs>
    var baseNotGenericType = typeof(GenericType<,,>);
    var baseType = baseNotGenericType.MakeGenericType(typeBuilder, typeof(TSource), typeof(TEventArgs)); 
    typeBuilder.SetParent(baseType);


    // the base class contains one constructor with string as param
    var baseCtor = baseNotGenericType.GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, new[] { typeof(string) }, null);

    var ctor = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard | CallingConventions.HasThis, new Type[0]);
    var ilGenerator = ctor.GetILGenerator();

    // i want to call the constructor of the baseclass with eventName as param
    ilGenerator.Emit(OpCodes.Ldarg_0); // push "this"
    ilGenerator.Emit(OpCodes.Ldstr, eventName); // push the param
    ilGenerator.Emit(OpCodes.Call, baseCtor);
    ilGenerator.Emit(OpCodes.Ret);

    var type = typeBuilder.CreateType();

    // return ...
}

On call of the constructor i'm getting a BadImageFormatException. What am i doing wrong?

As requested:

The BaseClass looks something like this:

public abstract class GenericType<GT, TEventSource, TEventArgs> : BaseClass
    where GT: GenericType<GT, TEventSource, TEventArgs>, new()
    where TEventArgs : EventArgs
    where TEventSource : class
{
    protected GenericType(string eventName)
    {
        _eventName = eventName;
    }
    // ...
}

What i would like to have as a result in runtime:

public class MyType : BaseClass<MyType, ConcreteSourceType, ConcreteEventArgsType>
{
    protected MyType() : base("SomeName")
    {

    }
}

Answer 1

I think the problem is that you're trying to call the constructor of the open generic type GenericType<GT, TEventSource, TEventArgs>, but you need to call the constructor of the closed type BaseClass<MyType, ConcreteSourceType, ConcreteEventArgsType>. The solution to the seems simple:

var baseCtor = baseType.GetConstructor(
    BindingFlags.NonPublic | BindingFlags.Instance, null,
    new[] { typeof(string) }, null);

The problem is that this doesn't work and throws NotSupportedException. So, it seems getting the constructor of a generic type, where one of the parameters is a TypeBuilder is nut supported.

Because of that, I think what you want is not possible using Reflection.Emit, unless there is some hack to work around this.

EDIT: A-HA! I had to dive deep into Reflection.Emit in Reflector _{^{(although looking at the right place in the documentation would have worked too)}}, but I found it: there is a special method exactly for this: the static TypeBuilder.GetConstructor(). So this should work:

var baseNonGenericCtor = baseNotGenericType.GetConstructor(
    BindingFlags.NonPublic | BindingFlags.Instance, null,
    new[] { typeof(string) }, null);
var baseCtor = TypeBuilder.GetConstructor(baseType, baseNonGenericCtor);

Answer 2

The easiest way to do this would be to compile up your abstract and derived classes into a simple assembly, then open them in Reflector using the "Reflection.Emit" language available as a addin from:

http://reflectoraddins.codeplex.com/

Yes, that's as cool as it sounds :)