How to call a method located inside a C# DLL, from VB.Net, with late binding

Question

I can't get a grip on how the various "Init", "Accumulate" ... methods work, to enable calling a method located inside a DLL, from VB.Net code.

Let's say the method to call has the following signature :

public double ComputeMeanPosition(ref SortedList<DateTime, double> posByTime)

Would you please kindly point me to an actual example of the use of the methods, or simply give me a few hints as how to actually pass the parameters to the method, call it and fetch the results ?

@Olivier Jacot-Descombes: I definitely prefix the class name by the namespace name, but yet fail to be able to reach the object. In fact I am surprised that your kind suggestion does not involve the following methods, displayed through introspection of the loaded DLL :

Type: MyClassName
        Method: Void Init()
        Method: Void Accumulate(System.Data.SqlTypes.SqlDouble, System.Data.SqlTypes.SqlDateTime, System.Data.SqlTypes.SqlBoolean)
        Method: Void Merge(MyClassName)
        Method: System.Data.SqlTypes.SqlDouble Terminate()
        Method: Void Write(System.IO.BinaryWriter)
        Method: Void Read(System.IO.BinaryReader)
        Method: Boolean Equals(System.Object)
        Method: Int32 GetHashCode()
        Method: System.String ToString()
        Method: System.Type GetType()

EDIT

In fact I have a code similar to the following one, that successfully manages to inspect the DLL and gets several types and methods out of it, giving the following results above for the method I would like to call.

Here is the code

        For Each oneModule As Reflection.Module In useAssembly.GetLoadedModules()
            Console.WriteLine("   - " & oneModule.Name)
            For Each oneType As System.Type In oneModule.GetTypes()
                Console.WriteLine("     Type: " & oneType.Name)
                For Each oneField As Reflection.FieldInfo In oneType.GetFields()
                    Console.WriteLine("        Field: " & oneField.ToString())
                Next oneField

                For Each oneMethod As Reflection.MethodInfo In oneType.GetMethods()
                    Console.WriteLine("        Method: " & oneMethod.ToString())

                    [[ ADD "Invoke" here ?]]
                Next oneMethod
            Next oneType
        Next oneModule

At the end, it seems that the [[...]] is at the place where the Invoke method should be called to call the method of my choice, but that is where I'm stuck... Would I need to build an object before calling it ? How should I pass it the parameters ? How to get the result ?

Answer 1

Something like this should work:

using System;
using System.Reflection;
using System.IO;

public class MainClass
{
      public static int Main(string[] args)
      {
           Assembly a = null;
           try
           {
                a = Assembly.Load("YourLibraryName");
           }
           catch(FileNotFoundException e)
               {Console.WriteLine(e.Message);}

           Type classType = a.GetType("YourLibraryName.ClassName");

           object obj = Activator.CreateInstance(classType);

           object[] paramArray = new object[1];    
           paramArray[0] = new SortledList<DateTime, double>();
           MethodInfo mi = classType.GetMethod("ComputeMeanPosition");
           mi.Invoke(obj, paramArray);

           return 0;
       }
 }

For VB.NET:

Imports System
Imports System.Reflection
Imports System.IO

Public Class MainClass
    Public Shared Function Main(args As String()) As Integer
        Dim a As Assembly = Nothing
        Try
            a = Assembly.Load("YourLibraryName")
        Catch e As FileNotFoundException
            Console.WriteLine(e.Message)
        End Try

        Dim classType As Type = a.[GetType]("YourLibraryName.ClassName")

        Dim obj As Object = Activator.CreateInstance(classType)

        Dim [paramArray] As Object() = New Object(0) {}
        [paramArray](0) = New SortledList(Of DateTime, Double)()
        Dim mi As MethodInfo = classType.GetMethod("ComputeMeanPosition")
        mi.Invoke(obj, [paramArray])

        Return 0
    End Function
End Class

Tested and this worked:

 Dim a As Assembly = Nothing
    Try
        a = Assembly.Load("TestLib")
    Catch ex As FileNotFoundException
        Console.WriteLine(ex.Message)
    End Try

    Dim classType As Type = a.[GetType]("TestLib.Class1")

    Dim obj As Object = Activator.CreateInstance(classType)

    Dim [paramArray] As Object() = New Object(0) {}
    [paramArray](0) = New SortedList(Of DateTime, Double)()
    Dim mi As MethodInfo = classType.GetMethod("ComputeMeanPosition")
    mi.Invoke(obj, [paramArray])

Answer 2

You can call this method as if was declared like this in VB

Public Function ComputeMeanPosition( _
    ByRef posByTime As SortedList(Of DateTime, Double)) As Double

---

Note: I used this online snippet converter to convert the C# code to VB. You have to add an empty method body {} to the C# method header before converting it.

public double ComputeMeanPosition(ref SortedList<DateTime, double> posByTime) {}

---

As this method is not declared as static in C# (Shared in VB) you first need to create an object. The method is most likely declared inside a class. Let's say the class was named "MyClass", then you would have to write something like this

Dim posByTime = New SortedList(Of DateTime, Double)()
Dim obj = New MyClass()
Dim result As Double = obj.ComputeMeanPosition(posByTime)

If the constructor (the New method) declares arguments, you will have to pass them when creating the object

Dim obj = New MyClass(arg1, arg2, ...)

Depending on what ComputeMeanPosition expects, you will have to add items to the list posByTime before calling it.

---

If the method was declared as static in C# (Shared in VB), you would qualify it with the class name, instead of creating an object.

Dim posByTime = New SortedList(Of DateTime, Double)()
Dim result As Double = MyClass.ComputeMeanPosition(posByTime)

---

UPDATE

If you load the assembly dynamically you will probably do something like this

Dim ass As Assembly = Assembly.LoadFrom("C:\SomePath\MyDll.dll")
Dim obj As Object = ass.CreateInstance("MyClass", True) 

Dim posByTime = New SortedList(Of DateTime, Double)()
Dim result As Double = obj.ComputeMeanPosition(posByTime)

And you will have to set the Option Strict Off for late binding.

---

If the constructor requires arguments, you will have to pass them to another overload of CreateInstance

Dim args = new Object() { arg1, arg2, ... }
Dim obj As Object = ass.CreateInstance("MyClass", True, _
    BindingFlags.Public Or BindingFlags.Instance, Nothing, Nothing, _
    args, Nothing, Nothing)

Answer 3

This is not the actual code, because I'm not in sitting in front of an actual c# editor, but something like this

// using System.Reflection required

// first load the external assembly into the appdomain and 
// create an instance of the object
var assembly = Assembly.Load("Path to the Assembly");
var type = assembley.GetType("TheNameOfTheClass");
var ctor = type.GetConstuctor();
var object = ctor.Invoke(); // assuming an empty construtor, else you'll need to pass in data

// next invoke the method
var methodInfo = assembly.GetMethodByName("ComputeMeanPosition");
var param = new SortedList<DateTime, double>();
var result = methodInfo.Invoke(object, new object[] { param });