How Can I Create a COM Interop Component from a C# DLL for Use in VB6?

Generating a COM Interop Component from a Simple C# DLL for VB6 Consumption

Background

Integrating C# code into legacy VB6 applications often requires exposing the C# functionality as a COM interop component. This allows VB6 programs to access and utilize the C# objects and methods.

Solution

Creating the C# DLL

1. Create a C# class library project.
2. Define an interface for the desired properties/methods and another interface for events.
3. Assign GUID attributes to the class and interfaces as specified in MSDN.
4. Enable COM visibility by checking "Make assembly COM-Visible" in Project Properties > Application > Assembly Information.
5. Set "Platform target" to x86 in Project Properties > Build.

Registering the DLL

Development Machine

1. Register the DLL during build by checking "Register for COM Interop" in Project Properties > Build.

2. Manually register using RegAsm from an administrator command shell:

   • RegAsm.exe -tlb -codebase mydll.dll

VB6 Application

1. Add a reference to the registered COM DLL in VB6.
2. Use Intellisense to access and utilize the exposed objects and methods.

Installer Integration (Using InstallShield)

1. Create a Component in InstallShield, associate it with a Feature, and enable ".NET COM Interop."
2. Add the DLL file to the Component, mark it as a Key File, and uncheck "Self-Register."
3. Add the TLB file to the Component and enable "Self-Register."
4. Ensure that the target machine has the appropriate .NET Framework installed.

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