I'm trying to create a VB wrapper for an exported DLL function. I believe I've set
up everything correctly, but I keep getting this error:

Server Error in '/' Application.
--------------------------------------------------------------------------------

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web
request. Please review the stack trace for more information about the error and where it
originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance
of an object.


My VB code for the compiled wrapper. For my purposes, test.dll has an exported
function called MyGetString that takes a pointer to a structure:


Imports System.Runtime.InteropServices

< StructLayout( LayoutKind.Sequential, CharSet := CharSet.Ansi )> _
Public Structure MYSTRUCT
   Public StrIn As System.String
   Public StrOut As System.String
End Structure

Public Class LibWrapper
   Declare Function MyGetString Lib "test.dll" _
   ( <[In], Out> ByVal InOutParams As MYSTRUCT ) As Integer
End Class


VBC Compiler:
vbc.exe /t:library /r:System.dll test.vb /out:test.dll


My VB script:

 Dim P as MYSTRUCT
 Dim Obj as LibWrapper

 P = new MYSTRUCT
 P.StrIn = "Test"

 Obj = new LibWrapper
 Obj.MyGetString(P)


The error is flagged on this line:
>>Obj.MyGetString(P)


Doesn't the new operator create an instance to an object? If so, why
isn't this working?

Ok, I got rid of visual basic and aspx, and wrote it as a C# program.

And I'm getting the same error message!
"Object reference not set to an instance of an object."

What the heck is this error??


My source:

using System;
using System.Runtime.InteropServices;
using System.Text;

public class TestClass {

       [DllImport("test.dll")]
       public static extern void MyGetString(string s1, ref string s2);

       [STAThread]
       public static void Main(string[] args) {

          string s1 = "teststring1";
          string s2 = "teststring2";

          try {
             MyGetString( s1, ref s2 );

             Console.WriteLine(" s1: {0}", s1 );
             Console.WriteLine(" s2: {0}", s2 );
          }
          catch (Exception e) {
             Console.WriteLine("Exception Message: " + e.Message );
          }
      }
}


My compiler:
csc.exe /reference:System.dll /out:test.exe test.cs

Got it working! Woohoo!

so.....how did you fix it?