VB6 UI Modernization: Replacing ActiveX Controls with .NET Core Components

Understanding VB6 COM Interop Challenges

Before jumping into migration strategies, it’s critical to understand the underlying challenges of working with VB6 COM components in a modern .NET Core environment. COM Interop is not just a technical bridge between platforms it’s a fundamental mismatch between two vastly different runtime models, architectures, and development philosophies.

Why COM Interop Is a Problem in .NET Core

COM Interop was originally designed to facilitate communication between unmanaged COM components and .NET Framework applications. However, .NET Core (and now .NET 5 and later) introduces a cross-platform, high-performance runtime that does not natively support COM in the same way. Key limitations include:

• Lack of built-in COM registration support on non-Windows platforms
• Limited tooling for type library generation and consumption
• Compatibility issues with legacy ActiveX controls and unmanaged DLLs
• Increased risk of runtime COMException errors due to binding issues

In many cases, the complexity and fragility of COM Interop can outweigh any short-term benefit of preserving legacy components.

Key Differences Between VB6 COM and .NET Core

Understanding the architectural differences between VB6 and .NET Core is essential for planning a successful migration. Some of the most important distinctions include:

Feature	VB6 COM	.NET Core
Memory Management	Manual (reference counting)	Automatic (Garbage Collection)
Component Registration	Registry-based (COM class registration)	Assembly-based (no registry dependency)
Cross-Platform Support	Windows only	Cross-platform (Windows, Linux, macOS)
Late Binding	Widely used (e.g. CreateObject)	Discouraged, limited dynamic support
UI Technology	ActiveX, Forms	WinForms, WPF, Blazor, MAUI

These differences affect how components are instantiated, managed, and executed. They also inform decisions around replacement strategies and tooling.

Common VB6 COM Components That Need Replacement

Some legacy COM components are more problematic than others and frequently require modernization. Examples include:

• ActiveX Controls: UI elements like MSFlexGrid, CommonDialog, or custom OCX controls that are no longer supported
• ADODB.Recordset: Used for database interaction, often replaced by DataTable, Entity Framework, or Dapper
• FileSystemObject: Used for file manipulation, typically replaced by System.IO in .NET
• Winsock: Networking functionality, now superseded by System.Net.Sockets
• Custom DLLs and Type Libraries: Require TlbImp.exe or full rewrites depending on complexity

Identifying these components early in the planning process helps you prioritize which modules need to be rewritten, wrapped, or refactored.

Strategies for Replacing COM Interop

To modernize a VB6 application, it is essential to decide how to handle existing COM components. Not all components require the same migration path. Some can be rewritten, others temporarily wrapped, and some are best served by adopting modern communication models like gRPC or REST. Below are three common strategies:

• Rewriting COM components in .NET Core
• Using interop wrappers for transitional support
• Replacing cross-process communication with modern protocols

Each option depends on your project’s timeline, available resources, and technical constraints.

Option One: Rewrite COM Components in Native .NET Core

Rewriting is the cleanest, most future-proof option. This means building a new .NET Core implementation to replace the original VB6 COM component, using modern libraries and architecture patterns.

When to choose this approach:

• The component has minimal external dependencies
• The business logic is well understood
• You want to eliminate COM registration entirely

Sample use case:

A VB6 component calculates monthly financial reports and exports them to Excel. Instead of using the legacy Excel COM API, you can create a .NET Core class using a library like EPPlus to generate reports in XLSX format. This new component can integrate into a larger web API or desktop application without any COM dependency.

Advantages:

• No need for COM registration or compatibility hacks
• Improved maintainability and testability
• Full use of .NET Core’s memory management and async features

Caution points:

• May require significant refactoring effort
• Some functionality might be tightly coupled to VB6 UI or state

Option Two: Use Interop Libraries When Rewrite Is Not Feasible

In situations where rewriting is too risky or time-consuming, interop wrappers allow you to continue using the VB6 COM components inside a .NET Core application on Windows.

When to use this approach:

• You lack source code for the original COM component
• The component interfaces with specialized hardware or third-party software
• You need a short-term solution during phased migration

Sample use case:

An existing COM component reads data from a legacy barcoding device. Rewriting it is impractical due to device firmware constraints. Instead, the development team uses TlbImp.exe to generate an interop assembly, allowing the .NET Core app to call into the COM interface without modifying the underlying functionality.

Implementation checklist:

• Use TlbImp.exe to import the type library
• Register the COM DLL using regsvr32 during setup
• Limit deployment to Windows platforms only

Trade-offs to consider:

Pros	Cons
Quick integration	Windows only
Minimal code changes	Higher chance of runtime errors
Supports legacy binaries	Cannot take full advantage of .NET features

Option Three: Migrate Cross Process Logic to gRPC or REST

When a COM component is used for communication between two applications, replacing it with a gRPC or REST service is often the best long-term solution. These approaches support modern, scalable software design with loose coupling between services.

When this makes sense:

• Your VB6 application calls into external services via COM
• You are transitioning to a microservices architecture
• You want platform independence

Sample scenario:

A VB6 point-of-sale application calls a COM service to get inventory stock levels. The service is replaced with a gRPC microservice hosted in .NET Core. Now, both the legacy frontend and a new web dashboard can access inventory data through the same interface.

gRPC vs REST comparison:

Feature	gRPC	REST
Performance	High	Moderate
Payload format	Binary (Protobuf)	Text (JSON)
Use case	Internal services	Public APIs or broad compatibility

Benefits of this approach:

• Avoids COM altogether
• Opens up cross-platform compatibility
• Encourages modular, testable architecture

Challenges:

• Requires significant redesign
• May need new client implementations

Step by Step Replacement Guide

Migrating a VB6 application to .NET Core is a process that requires both planning and precision. While the idea of “lift and shift” sounds appealing, real-world systems rarely allow such simplicity. VB6 applications tend to be deeply interwoven with COM components, legacy ActiveX controls, and loosely typed design patterns that no longer map cleanly to modern .NET practices.

Instead of attempting a full rewrite in one pass, a phased approach based on structured steps can help reduce risk and improve reliability. By isolating core tasks—such as analyzing dependencies, replacing UI components, and managing dynamic object creation—you can ensure that each part of the application transitions safely and with minimal disruption.

This section outlines a clear workflow to help guide that transition. Whether you’re working on a single module or preparing an entire suite for modernization, these steps will form the foundation of a successful COM interop replacement strategy in .NET Core.

Step One: Analyze COM Dependencies in the Existing VB6 Application

The first step in any migration is understanding what COM objects are present and how they are used. VB6 applications often rely on a mix of built-in components, third-party ActiveX controls, and in-house COM libraries. Each of these might be referenced in forms, modules, or dynamically created at runtime.

Begin by reviewing the VB6 project files to extract all declared references. You can use tools to browse registered COM objects on a system and identify those used by your application. These tools expose class IDs, method definitions, and interfaces, which helps determine how tightly coupled the VB6 code is to specific COM objects.

Another helpful tool is the Visual Basic project explorer itself. Look for lines that use CreateObject, GetObject, or any automation logic. Often, these calls are buried in event handlers or utility modules. The goal is to create an inventory of dependencies so you can classify them as candidates for replacement, wrapping, or full removal.

For example, if you find repeated use of CreateObject("Scripting.FileSystemObject"), you already know to target that component later with a .NET System.IO replacement. If you encounter references to a custom-built library such as AccountingLib.AccountEngine, you will need to track down the source code or DLL to determine feasibility of conversion.

Step Two: Replace ActiveX Controls with Modern .NET UI Components

Once dependencies are cataloged, your next task is modernizing the user interface layer. VB6 forms often embed ActiveX controls, especially for grid views, dialogs, and special input handling. Many of these components are no longer supported and must be replaced to ensure compatibility with modern UI frameworks.

A common example is the MSFlexGrid, used for displaying tabular data. This control can be replaced by DataGridView in WinForms or a DataGrid in WPF, depending on which .NET Core UI technology you choose. These replacements offer better customization and support modern data binding techniques. Keep in mind that layout and event behavior may differ, so rewrites should be validated against the original control behavior.

Another frequent case is the CommonDialog control, which offers file selection, color pickers, and printer dialogs. In .NET Core, these are typically handled through OpenFileDialog, SaveFileDialog, and related components from the Windows Forms library. While the functionality is equivalent, some properties or dialog customizations may require extra effort to replicate.

Plan to gradually rebuild the UI one control at a time, especially in applications with complex forms or embedded COM objects. Begin with low-risk screens that are less dependent on business logic, then move toward those with heavier functionality once you gain confidence in the process.

Step Three: Handle Late Binding and Dynamic Object Creation

VB6 makes frequent use of late binding through the CreateObject function. This allows developers to dynamically load COM objects at runtime without early binding or type safety. While this was flexible in the VB6 environment, it introduces challenges when migrating to .NET Core, which favors strongly typed, compiled object instantiation.

To replicate this functionality in .NET Core, you have a few options. The most direct equivalent is Activator.CreateInstance, which allows you to instantiate objects from an assembly dynamically. This works well for scenarios where you still depend on COM wrappers or are using reflection for plug-in like behavior. However, it comes with trade-offs in performance and maintainability.

If the original use of CreateObject was simple, such as spawning a utility class or helper object, the better path is to convert it to a direct constructor call. This allows you to take advantage of dependency injection and interface-based programming, which are standard in modern .NET design.

In cases where you still need to load assemblies at runtime, Assembly.Load or Assembly.LoadFrom can be used. These methods let you scan and execute types from DLL files programmatically. However, they should be used sparingly and with caution, especially in production scenarios, as debugging dynamically loaded components can be difficult.

For example, if your VB6 app includes a line like Set engine = CreateObject("Legacy.AccountEngine"), the .NET version might involve defining an interface for IAccountEngine, implementing the engine logic in a .NET class, and injecting it through the application’s service container. This results in better code structure and testability.

Handling Specific COM Scenarios

While general strategies for replacing COM interop are helpful, many VB6 applications rely on specific components that require special treatment during migration. These include data access layers, file operations, and network communication tools that were tightly integrated into the VB6 environment. Handling these properly is essential for preserving application behavior while upgrading to modern .NET Core architecture.

This section provides practical guidance on how to replace some of the most common COM-based components found in VB6 projects. By examining how they work and what modern equivalents exist, you can avoid common pitfalls and streamline the migration process.

Replacing ADODB Recordset with Modern Data Access in .NET Core

One of the most heavily used components in VB6 applications is the ADODB Recordset, which was the standard for interacting with databases using ActiveX Data Objects. In VB6, developers often relied on Recordset for iterating over rows, performing cursor-based logic, and binding data directly to UI controls.

In .NET Core, the recommended approach is to use DataTable, DbDataReader, or an object-relational mapper such as Dapper or Entity Framework Core. These tools offer strong typing, async support, and safer memory management. For developers who need fine-grained control, ADO.NET with SqlCommand and SqlDataReader provides a close procedural match to the Recordset pattern, without the overhead of full ORM frameworks.

For example, a legacy block of VB6 code that opens a Recordset with a SQL query and loops through records can be rewritten in .NET Core using using statements and strongly typed models. Developers must also be aware of differences in cursor behavior, locking mechanisms, and transaction handling between ADO and modern data access methods.

If a Recordset was used for disconnected data manipulation, consider replacing it with a DataTable that can be populated and modified locally. In more modern scenarios, asynchronous LINQ queries and projection into view models offer a cleaner, testable structure.

Converting FileSystemObject to System.IO in .NET Core

Another frequent dependency in VB6 is the use of the FileSystemObject for file and folder operations. This object provided methods like CopyFile, CreateFolder, and GetFile, and was often used for reading and writing text files or navigating directory structures.

In .NET Core, the System.IO namespace fully replaces this functionality and offers a more powerful and safer API. Classes like File, Directory, and Path provide static methods for file manipulation, while FileStream and StreamReader allow for more advanced use cases.

For example, a VB6 snippet such as fso.CopyFile "source.txt", "target.txt" can be directly translated into File.Copy("source.txt", "target.txt") in C#. Additional benefits include support for exception handling, cross-platform file access, and better performance through buffered streams.

Unicode path handling is also significantly improved in .NET Core. Unlike older VB6 code that might break on long or multibyte filenames, .NET Core fully supports modern file systems, including extended paths and UTF encoding.

During migration, it is important to inspect all uses of FileSystemObject, including implicit references in helper modules or shell scripts. Consider replacing entire file-handling workflows with standardized utility classes in .NET Core, which improves reusability and testability.

Migrating VB6 Winsock to System.Net.Sockets

Networking code in VB6 often relied on the Winsock control for sending and receiving TCP or UDP messages. This control was easy to use in event-driven forms and commonly appeared in client-server or real-time monitoring applications. Unfortunately, Winsock is not supported in .NET Core and has no direct equivalent in the new runtime.

The modern approach is to use the System.Net.Sockets namespace, which provides low-level control over TCP and UDP communication. Developers can create TcpClient and TcpListener instances to manage connections, and use asynchronous read and write methods to handle traffic efficiently.

For example, a VB6 application that connects to a remote telemetry server over TCP can be recreated in .NET Core using a background service that connects using TcpClient, reads incoming data with a NetworkStream, and processes it asynchronously.

One important shift is the change from synchronous to asynchronous event handling. Unlike Winsock, which relied on form-level events, .NET Core promotes non-blocking communication with async and await, which improves scalability and responsiveness.

When migrating, developers should also implement proper timeout handling, reconnection logic, and message framing. These patterns are critical for ensuring that the new implementation is robust under real-world conditions.

Testing and Debugging COM Interop Replacements

Replacing COM components in a VB6 migration is not just about compiling new code. It is about ensuring that the new behavior aligns with what the old system delivered, often in subtle and undocumented ways. Testing and debugging take on even greater importance when dealing with systems that have evolved over time, carry business-critical functions, and interact with other legacy components that may still be active.

VB6 allowed for a more forgiving runtime model. Errors were often caught late, type safety was minimal, and exception handling was sometimes absent altogether. In contrast, .NET Core provides strong typing, structured error handling, and powerful testing frameworks. This shift is positive, but it also means that previously hidden bugs or inconsistencies might now surface during the migration process.

This section explores practical approaches to ensuring that COM interop replacements behave reliably. It covers strategies for writing unit tests for migrated components, debugging interop-specific errors such as COM exceptions, and using modern logging tools to trace and diagnose issues. Whether your goal is functional parity, increased performance, or greater testability, the tools and practices described here will help validate each replacement step with confidence.

Unit Testing Migrated Components

Unit testing in .NET Core allows developers to validate components in isolation, which is especially useful when replacing business logic previously embedded in COM libraries. Migrated classes should be designed with interfaces, making them easier to test with modern frameworks such as xUnit or NUnit.

For example, if a VB6 function responsible for validating invoice totals has been rewritten in C#, that method should be extracted into a service and covered by unit tests for different edge cases.

To avoid dependencies on legacy code during tests, developers can use mocking tools to simulate the behavior of external services or database calls.

Common mocking libraries include:

• Moq (for interface-based mocking)
• NSubstitute (for flexible, fluent test syntax)
• FakeItEasy (for easy-to-read test doubles)

A test might look like this using Moq:

var mockRepo = new Mock<IInvoiceRepository>();
mockRepo.Setup(x => x.GetTotal("INV001")).Returns(1200);

var service = new InvoiceValidator(mockRepo.Object);
bool result = service.ValidateMinimum("INV001", 1000);

Assert.True(result);

By isolating dependencies like databases or file access, tests can focus on logic, leading to higher confidence and faster iteration during refactoring.

Debugging Interop Issues

Even with best practices, some COM replacement efforts introduce runtime problems that require thorough debugging. These problems can come from improper type conversions, incomplete wrappers, or mismatches in runtime behavior compared to VB6.

One of the most common errors encountered during interop transitions is the COMException. This exception generally indicates a failure to create or invoke a legacy component. When debugging these issues, always begin by confirming that the COM DLL is properly registered and that the generated interop assembly is being loaded by your .NET Core application.

To diagnose these errors, it helps to log the specific error codes and messages returned by the exception:

try
{
    var legacy = new LegacyComWrapper();
    legacy.Execute();
}
catch (COMException ex)
{
    Console.WriteLine($"COM error: {ex.Message} (HRESULT: {ex.HResult:X})");
}

Use the HRESULT code to identify common causes such as missing registry entries, class ID mismatches, or version conflicts. Microsoft’s official documentation and tools like OLEView and Process Monitor can help trace these errors to their source.

Logging and Tracing Interop Behavior

Proper logging is essential when validating the behavior of COM replacements, especially in larger applications with dozens of migrated modules. Implement structured logging at key transition points, including the initialization of legacy wrappers, the execution of imported methods, and any internal error handling.

Modern logging frameworks like Serilog and NLog make it easy to capture structured logs that can be filtered and reviewed during debugging sessions. Consider tagging logs from legacy-related components with unique categories to make them easier to track.

For example, when replacing an ActiveX chart control with a native .NET charting library, log both the input data and rendering parameters, so any visual inconsistencies can be traced to a data or binding issue.

In staging environments, it may also be useful to add tracing logic that compares the outputs of the original COM component and the new .NET implementation, to ensure behavioral parity before the final cutover.

Performance and Optimization

After replacing COM components with native .NET Core code, performance becomes a central focus. While modern frameworks often outperform legacy counterparts, performance gains are not guaranteed without deliberate tuning. In fact, the transition from COM to managed code can introduce overhead, especially if wrappers, compatibility layers, or reflection are used without careful consideration.

This section discusses how to measure performance differences between the old and new implementations, what to watch for in terms of runtime behavior, and how to optimize memory usage and interop boundaries. Improving responsiveness, reducing latency, and aligning memory patterns with .NET Core’s garbage collection model are essential steps toward a production-ready system.

Benchmarking COM and .NET Core Performance

Before attempting to optimize, it is important to establish a clear baseline. Benchmarking helps identify which parts of the application have become slower, faster, or stayed consistent after migration. In legacy VB6 environments, performance was often measured informally through user perception or stopwatch-style testing. .NET Core, by contrast, supports detailed benchmarking tools.

You can use BenchmarkDotNet to measure performance of migrated components. This tool runs isolated performance tests with warm-up iterations, statistical analysis, and memory profiling. A simple benchmark might look like this:

[MemoryDiagnoser]public class ReportGenerationBenchmark
{
    private readonly ReportService service = new ReportService();

    [Benchmark]    public void GenerateQuarterlyReport()
    {
        service.Generate("Q2");
    }
}

This type of test can show how a modern C# implementation compares to a previous COM routine in terms of execution time, memory allocation, and consistency. Focus your benchmarks on areas where users have historically reported lag or instability.

Reducing Overhead in Interop Scenarios

If some COM components still remain, such as wrapped DLLs or ActiveX controls, you may notice performance degradation. This is often caused by the marshaling required to translate calls between managed and unmanaged environments. Marshaling adds memory pressure, slows execution, and introduces potential type conversion errors.

To reduce this overhead:

• Avoid frequent calls across the interop boundary in performance-critical loops
• Cache references to COM objects instead of creating them repeatedly
• Use explicit marshalling only when needed, rather than relying on automatic conversions

For example, instead of calling a COM method inside a loop like this:

for (int i = 0; i < records.Count; i++)
{
    legacyCom.SetValue(i, records[i].Value);
}

It may be more efficient to batch the values or move processing into the COM component itself, if modifying it is still possible.

Even better, replace these interop calls entirely with .NET equivalents, especially if profiling confirms they are responsible for bottlenecks.

Understanding Memory Management Differences

In VB6 and COM, memory was largely managed through reference counting. Objects were released when their reference count dropped to zero, which worked well in theory but often led to circular references and memory leaks. Developers had to manually call Set object = Nothing and hope for proper cleanup.

.NET Core uses garbage collection, which frees developers from manual reference tracking but introduces different patterns. Objects are not disposed of immediately after use unless explicitly handled through IDisposable. In applications that replace COM objects with disposable .NET resources, proper disposal is crucial.

If your migrated system uses database connections, file handles, or memory buffers, wrap those components in using blocks or implement a clear disposal strategy. Otherwise, memory usage may grow unpredictably, especially under heavy workloads.

Here is a safe pattern for handling a migrated file export operation:

using (var writer = new StreamWriter("output.csv"))
{
    foreach (var record in data)
    {
        writer.WriteLine(record.ToCsv());
    }
}
 These insights are especially helpful when troubleshooting performance issues in production or under load.

Fallback Strategies

In some cases, a full migration from VB6 to .NET Core is not immediately possible. Applications may rely on third-party COM components with no modern equivalent, contain business rules locked inside opaque code, or operate in environments where downtime for rewriting is unacceptable. In these situations, fallback strategies allow development teams to modernize incrementally without breaking existing systems.

This section outlines approaches for running VB6 and .NET Core side by side, using compatibility layers such as COM+, and maintaining stability while building toward full modernization. These strategies are not long-term solutions, but they help reduce risk and preserve business continuity during a staged migration.

Running VB6 and .NET Core Applications Together

One of the simplest fallback options is to run the original VB6 application alongside new .NET Core modules. This can be accomplished by launching .NET Core processes from VB6 using shell commands or by establishing communication between processes using intermediate files, sockets, or local web services.

For example, a VB6 desktop system might handle UI interactions while calling a background .NET Core console application to generate reports, perform calculations, or integrate with cloud APIs. This method keeps the legacy interface intact while enabling access to newer functionality and services.

To facilitate this hybrid operation, developers often use:

• Command-line arguments for launching helper utilities
• Named pipes or sockets for bidirectional messaging
• Temporary files or databases for data handoff between runtimes

This approach is particularly helpful when existing users are trained on the VB6 interface and cannot immediately transition to a new system.

Using a COM Plus Layer for Gradual Migration

In scenarios where both the VB6 application and the new .NET Core modules must share logic, a transitional layer using COM Plus (COM+) can provide a bridge. This method involves wrapping .NET components as COM-visible libraries and registering them using regasm and tlbexp.

This makes it possible for VB6 code to instantiate .NET components as if they were native COM objects. Over time, business logic can be moved from VB6 modules into these .NET components, reducing the size and complexity of the VB6 codebase until it is ready to be retired.

Here is a simplified outline of the process:

1. Mark your .NET class with the [ComVisible(true)] attribute
2. Compile it as a class library and register it using regasm
3. Generate a type library with tlbexp and reference it in the VB6 project

While this solution introduces some maintenance complexity, it allows teams to modernize sensitive or critical functionality without a full rewrite.

Keep in mind:

• This only works on Windows platforms with COM registration support
• Debugging across environments requires additional setup
• Versioning must be handled carefully to avoid breaking the VB6 application

Fallback strategies are not meant to be permanent. They serve to reduce disruption and allow teams to focus on migrating high-priority areas first. With proper planning, even a partial fallback can help accelerate full modernization by delivering working features while retiring outdated components gradually.

Using SMART TS XL for COM Interop Replacement

Modernizing legacy VB6 applications is challenging, especially when COM interop is involved. Manual migration is time-consuming, risky, and often incomplete. SMART TS XL is a specialized automation platform designed to streamline and accelerate this process. It focuses on replacing COM components, ActiveX controls, and late-bound VB6 patterns with modern .NET Core code, offering both speed and accuracy without sacrificing stability.

This section explains the key capabilities of SMART TS XL, how it addresses the most complex parts of COM interop, and when it makes sense to incorporate it into your migration strategy. Whether you are just beginning to plan or already migrating specific modules, SMART TS XL can help you reduce manual effort, avoid critical errors, and improve long-term maintainability.

Key Challenges SMART TS XL Solves

SMART TS XL is purpose-built to handle the core pain points that slow down or block VB6 to .NET Core migrations. Its toolset automates many of the most repetitive and error-prone tasks developers face.

Key areas of support include:

• COM object replacement: Automatically maps VB6 COM components to equivalent .NET Core classes, reducing the need to reverse-engineer legacy code.
• ActiveX control migration: Replaces embedded controls like MSFlexGrid and CommonDialog with modern UI equivalents in WinForms or WPF.
• Late binding resolution: Converts CreateObject and similar dynamic patterns into strongly typed class instantiations.
• Data access modernization: Refactors ADODB and DAO patterns into ADO.NET, Entity Framework, or other standard data access approaches.
• Interop performance optimization: Minimizes marshaling and type conversion overhead in hybrid projects that still rely on some COM components.
• Automated code transformation: Applies consistent translation rules across the entire application, ensuring unified structure and fewer regressions.

By using SMART TS XL, teams avoid the need to maintain parallel COM and .NET Core versions of their codebase and reduce dependence on legacy runtime environments.

When to Consider SMART TS XL

SMART TS XL is best suited for medium to large applications where manual migration would take months or even years. It is particularly helpful when:

• The project has hundreds of forms or controls tied to legacy COM libraries
• Business logic is scattered across modules and relies heavily on dynamic object use
• Deadlines demand faster delivery with minimal functional regression
• In-house developers are not familiar with legacy VB6 internals or COM interop mechanics

For example, consider a manufacturing ERP system built in VB6 with dozens of custom reports and real-time machine interface components. Migrating this system manually would involve tracking undocumented COM objects, rewriting legacy charting controls, and restructuring business workflows. Using SMART TS XL, the team can generate equivalent .NET Core code for UI, logic, and data access layers, then refactor only what needs customization.

In another case, a financial services application relied heavily on VB6 class modules that accessed COM-based accounting engines. With SMART TS XL, those class modules were automatically converted into C# classes with dependency injection support, exposing clean APIs for newer .NET services.

Adopting SMART TS XL does not eliminate the need for testing or refactoring, but it dramatically reduces the scope of manual conversion work. This frees development teams to focus on optimization, UI redesign, and building new functionality rather than replicating the past line by line.

Modern Code, Modern Future: The End of COM Is the Start of More

Modernizing a VB6 application with COM interop is more than a technical migration—it is a strategic investment in long-term flexibility, maintainability, and scalability. As businesses move toward cross-platform systems, cloud-native architecture, and security-focused environments, leaving COM dependencies behind becomes a necessary step in future-proofing legacy applications.

Throughout this guide, we have explored why COM interop is difficult in .NET Core and how it differs from traditional VB6 behavior. We examined various migration strategies, reviewed how to handle common COM components like Recordset, FileSystemObject, and Winsock, and discussed practical methods for testing, debugging, and optimizing new code. We also introduced fallback options for hybrid deployments and explained how SMART TS XL can reduce the manual burden and accelerate the transition.

Successful migration depends on making clear decisions early, understanding what to rewrite and what to wrap, and applying modern engineering practices to each part of the application. Teams that approach this migration methodically will reduce risk and gain the full benefits of a modern .NET ecosystem.

Checklist for Full COM Interop Removal

To support your next steps, use this checklist to assess your readiness and progress:

• Have you audited all COM and ActiveX dependencies in the VB6 application?
• Have you categorized components as rewrite, wrap, or redesign candidates?
• Are all ActiveX controls mapped to equivalent .NET Core UI components?
• Have late-bound objects using CreateObject been replaced with typed alternatives?
• Are ADODB and DAO elements migrated to ADO.NET or ORM frameworks?
• Have you implemented test coverage for each migrated class or service?
• Is COM interop fully removed from your project references and build process?
• Have all file operations been ported to System.IO with Unicode support?
• Are legacy sockets replaced with System.Net.Sockets or HTTP-based protocols?
• If fallback methods were used, are they clearly documented and scheduled for removal?

By completing this checklist, you create a clear path to deprecating COM from your architecture. Whether you continue incrementally or make a full leap using tools like SMART TS XL, the goal remains the same turning a fragile, tightly coupled legacy system into a clean, modern application ready for future growth.