Invoke member through reflection passing derived class as argument - vb.net

Question

I'm trying to call the method 'MyMethod' of class 'CMyClass'. This method has a parameter of type "CBaseClass", and I'm passing an object of type "CDerivedClass".
Class CBaseClass
Public m_AMember As String
Sub MethodOne()
// DoSomething
End Sub
End Class
Class CDerivedClass
Inherits CBaseClass
Public m_MyMember As Integer
Sub MethodTwo()
// DoSomething
End Sub
End Class
Class CMyClass
Sub MyMethod(ByVal obj As CBaseClass)
// DoSomething
End Sub
End Class
Sub Main()
'load assembly
Dim objAssembly As Assembly = Assembly.LoadFrom("myfile.dll")
'create class instance and MethodInfo object
Dim t As Type = objAssembly.GetType("MyNamespace.CMyClass")
Dim obj As Object = Activator.CreateInstance(t)
Debug.Assert(obj IsNot Nothing)
Dim m As MethodInfo = t.GetMethod("MyMethod")
Debug.Assert(m IsNot Nothing)
'Init arguments (only one)
Dim par As New CDerivedClass()
Dim parameters As Object() = New Object(0) {par}
'invoke method
m.Invoke(obj, parameters) '<<<< ArgumentException here!
End Sub
The argument exception says "object of type 'MyNamespace.CDerivedClass' cannot be converted to type 'MyNamespace.CBaseClass'.
I changed "ByRef" to "ByVal" in MyMethod signature, but nothing changed.
I tried to change type of 'par' object with:
Dim par As CBaseClass = New CDerivedClass()
without success.
How I can invoke correctly the method "MyMethod" with an instance of derived class?
Thank you very much.

Answer 1

I just tried your code in a stand alone project and it worked fine. I only adjusted the assembly line to get the current assembly instead of from a file, and I changed the name in GetType to reflect my namespace. My guess is that perhaps your DLL you are loading is out of date, or you have duplicate definitions of the classes in your calling assembly, and thats why it cannot do the type conversion.
Imports System.Reflection
Module Module1
Sub Main()
'load assembly
Dim objAssembly As Assembly = Assembly.GetExecutingAssembly()
'create class instance and MethodInfo object
Dim t As Type = objAssembly.GetType("ConsoleApplication1.CMyClass")
Dim obj As Object = Activator.CreateInstance(t)
Debug.Assert(obj IsNot Nothing)
Dim m As MethodInfo = t.GetMethod("MyMethod")
Debug.Assert(m IsNot Nothing)
'Init arguments (only one)
Dim par As New CDerivedClass()
Dim parameters As Object() = New Object(0) {par}
'invoke method
m.Invoke(obj, parameters) '<<<< No ArgumentException here!
End Sub
End Module
Class CBaseClass
Public m_AMember As String
Sub MethodOne()
End Sub
End Class
Class CDerivedClass
Inherits CBaseClass
Public m_MyMember As Integer
Sub MethodTwo()
End Sub
End Class
Class CMyClass
Sub MyMethod(ByVal obj As CBaseClass)
End Sub
End Class

Answer 2

Finally I solved using serialization...
So 'par' is the string containing the serialized object of type CDerivedClass in the calling project.
MyMethod is changed to:
MyMethod(xml_CBaseClass As String)
In dll project the string parameter xml_CBaseClass is deserialized creating an object of CBaseClass.
Note: since I have derived type, Deserialization of derived class give another problem. The solution is https://stackoverflow.com/a/590711/1315873
(I just made a little change, using StringWriter for serialization, StringReader for deserialization, instead of using MemoryBuffer).
CBaseClass has fixed derived types so I wrote them hard-coded, but to be flexible you can do something like:
Dim subTypes as New List(Of Type) '<- all classes derived from 'myType'
For Each t In myType.Assembly.GetTypes()
If t.IsSubclassOf(myType) Then
subTypes.Add(t)
End If
Next
CBaseClass and all its derivated classes must have constructor New() without parameters.
I load assemblies using LoadFrom() since I don't know their names (I use Dir() to get all them from a known fixed folder).