How to consume COM object in ASP.NET class file

Question

I have a COM object that I am trying to wrap in a C# class in order to make it more readily available for other applications that wish to consume it.

I have the following code that creates an instance of the COM object, and then using reflection makes a call to a method to retrieve user data. This code works fine when it is located in an aspx page.

object jdObj = Server.CreateObject("jd_api.UserCookie");
string username = jdObj.GetType().InvokeMember("GetUserName", System.Reflection.BindingFlags.InvokeMethod, null, jdObj , null).ToString();

However, when I move the code to a class file (JD_API.cs) in order to abstract it from the actual website, I can no longer get it to work. For example, I have the following static method that is declared like such:

public static string GetUserName() {

    object jdObj = Server.CreateObject("jd_api.UserCookie");
    string username = jdObj.GetType().InvokeMember("GetUserName",
System.Reflection.BindingFlags.InvokeMethod, null, jdObj , null).ToString();

    return username;
}

Unfortunately, the Server object is restricted to some ASP.NET libraries that are included by default in web applications, and so the above code was a no-go. So at this point I decided to try to create an instance of the COM object like such:

public static string GetUserName() {

    Type type = Type.GetTypeFromProgID("jd_api.UserCookie");
    object jdObj = Activator.CreateInstance(type);

    string username = jdObj.GetType().InvokeMember("GetUserName", System.Reflection.BindingFlags.InvokeMethod, null, jdObj , null).ToString();

    return username;
}

However at runtime I get an error that says, "Attempted to read or write protected memory. This is often an indication that other memory is corrupt.".

I'm not sure where to go from here. Any help on how to abstract creating an instance of this COM object to a layer that is not within the web application itself would greatly appreciated. Thanks!!

Answer 1

Declare DLL functions within a class. Then define a static method for each DLL function you want to call. The following code sample creates a wrapper named Win32MessageBox that calls the MessageBox function in User32.dll each time a .NET app calls the object Show method. It requeres the System.Runtime.InteropServices namespace.

using System;
using System.Runtime.InteropServices;

class Win32MessageBox
{
    [DllImport("user32.dll")]
    private static extern int MessageBox(IntPtr hWnd, String text,
        String caption, uint type);

    public static void Show(string message, string caption)
    {
        MessageBox(new IntPtr(0), message, caption, 0);
    }
}

To call it, just type:

Win32MessageBox.Show("StackOverflow!", "my stack box");

The method where you call the above line doesn't need to be aware that it's a actually calling a function in an unmanaged DLL.

Resources: the MCTS Self-Paced Training Kit (Exam 70-536) by Tony Northrup.

Answer 2

Hove you tried usinsing interoperating

I've done the following in the past (working from memory so you might need to fiddle with this a bit):

1. Right Click "References" in your project
2. Select "Add Reference"
3. Selelct the "Com" Tab
4. Find and add your Com Instnace

In your class file

using yourComName;

public static string GetUserName() 
{
        yourComName.yourComClass jdObj = new  yourComClass();
        string username = jdObj.GetUserName(someParameters);
        return username;
}

Hope this a) works and b) helps!