VB6 to .NET Core Migration

VB6 (Visual Basic 6) was released in 1998 as a beginner’s language and integrated development environment for developing Windows-based GUI applications. Developers and companies widely used it during the late 1990s and early years of the 21st century. However, as time went on, Microsoft officially ended support for VB6 in 2008.

Today, many companies continue to use VB6 applications to manage vital business processes. Since VB6 depends on operating systems, browsers, databases and other components, as the latter are gradually excluded from support, maintaining the VB6 applications becomes complicated and costly. Porting VB6 apps to more contemporary environments such as .NET Core has thus become a priority of many organizations, as evidenced by the increased adoption of the technology.

Benefits of Migrating from VB6 to .NET Core

Migrating aging VB6 to .NET Core offers many benefits:

Cross-Platform Support

.NET Core apps can run on Windows, Mac, and Linux systems. VB6 apps are limited to Windows. With .NET Core, you can reach a much wider audience.

Access to Modern Features

.NET Core supports the new features like cloud, container, HPC and machine learning. These modern technologies cannot be utilized in VB6 apps.

Lower Costs

Migrating will remove you from costly and old platforms .NET Core is free and built mostly with open-source tools, which helps minimize licensing and hosting expenses.

Prevent VB6 from Becoming a Broken Product

Since VB6 depends on old components, the applications can easily fail at any time with no prior notice. Migrating to .NET Core future-proof apps.

Improved Developer Productivity

.NET Core has very good support in development, along with good documentation and active community support. Locating VB6 help becomes more difficult annually.

Improved Security

According to the report, 92% of the firms assessed had in-house app vulnerabilities that led to a breach in the previous year.

.NET Core offers better security practices, such as encrypted connections, code signing, and sandboxing. As Windows security tightens, VB6 apps are increasingly vulnerable.

Challenges When Migrating VB6 to .NET Core

However, migrating VB6 to .NET Core poses some key challenges:

Significant Rewrites Required

VB6 and .NET Core are fundamentally different platforms. Parts of apps often need full rewrites to work correctly in .NET Core.

Testing Burden

With extensive changes, migrated apps require thorough regression testing to ensure correct functionality. Automated testing is highly recommended.

Training Developers on .NET Core

Developers skilled in VB6 must learn modern development practices to work with .NET Core efficiently. This requires training time and effort.

Porting Existing Data Access Code

Data access mechanisms in VB6 rely on outdated technologies like DAO and RDO. These must be replaced with modern .NET data access APIs.

Replacing Deprecated VB6 Controls

Visual controls in VB6 leveraged custom COM components. In. NET, these must be swapped with UI frameworks like Windows Forms or WPF.

Managing Interop Requirements

Apps may require VB6 and .NET Core versions to interoperate during a transition period. Interop brings further complexity.

Migration Process Overview

Migrating VB6 to .NET Core is a multi-step process. While every migration has unique considerations, the high-level process typically includes:

1. Conducting an Inventory Assessment

Catalog all existing VB6 applications and components. Review interdependencies and business criticality.

2. Setting Migration Priorities

First, determine which apps offer the greatest business value to migrate based on the assessment.

3. Choosing a Migration Strategy

Decide whether to migrate all at once or gradually migrate individual apps over several phases. Consider budgets, timelines, resource availability, and business needs.

4. Selecting a Migration Approach

Choose from strategies like full rewrites, automated conversions, or interoperability solutions to find the best fit per app.

5. Migrating Data Access Code

Data access mechanisms must be upgraded to use .NET data APIs like ADO.NET, Entity Framework, and Dapper.

6. Re-architecting UI Code

Replace VB6 UI features with .NET UI frameworks like Windows Forms, WPF, Blazor, or MAUI.

7. Reengineering Business Logic

.NET Core runs on .NET, not COM. So, business logic requires alterations to work correctly.

8. Establishing Integration Points

If maintaining an interop between VB6 and .NET Core, expose and call integration points between the two platforms.

9. Transitioning Supporting Tools

Upgrade build servers, test suites, monitoring stacks, and operations practices for .NET Core.

10. Testing and Quality Assurance

Rigorously test migrated apps to ensure all use cases function properly before re-deployment. Fix issues before going live.

Key Migration Approaches

Organizations generally utilize one or a combination of three main strategies to migrate VB6 applications to .NET Core:

Full Rewrites

With full rewrites, developers manually rebuild the entire application in .NET Core from the ground up. This allows taking full advantage of modern platforms and architectures. However, rewrites are time-consuming and skill-intensive.

Automated Conversions

Automated conversion tools translate VB6 code to C# on .NET frameworks like .NET Framework 4.x. This machine-generated code serves as a baseline for developers to tweak and optimize. It takes less manual effort than rewrites, but converted code is often inefficient.

Interoperability Solutions

Interop solutions integrate VB6 and .NET apps during a gradual transition. Simple interop proxies translate calls between COM and .NET without altering existing code, reducing initial cost and risk but prolonging modernization efforts.

Organizations often start with automated conversions and interop, then gradually rewrite components over multiple phases. This balances business needs with modernization goals. For simpler apps, wholesale rewrites may work best.

Migration Tools and Resources

Many tools and resources exist to assist with VB6 to .NET migrations:

Code Conversion Tools

1. Modernize Visual Basic by Mobilize.Net - Leading automated VB6 to .NET conversion platform
2. CARMA by Cincom - Automated code conversion tool
3. VB Migration Partner by Mobilize.Net - Semi-automated code migration

Interoperability Bridges

1. COM Interop - Built-in .NET feature to integrate COM/VB6 code
2. CCW (COM Callable Wrapper) - Call VB6 components from .NET
3. RCW (Runtime Callable Wrapper) - Call .NET components from VB6

Testing Tools

1. Visual Studio Test Suite - Automated testing framework
2. Selenium - Browser automation for web app testing
3. Telerik Test Studio - Automated functional and load testing

Development Frameworks

1. .NET Core - Modern open-source framework to replace VB6 runtime
2. Entity Framework - Modern data access framework
3. Windows Forms - UI framework to replace VB6 visual controls

Documentation

1. .NET 5 porting guidance - Official Microsoft .NET porting advice
2. .NET blog migration articles - Dev community migration lessons learned

Leveraging conversion tools, interop bridges, testing suites, and ample online documentation can help smooth out the VB6 to .NET Core migration journey.

Migration Best Practices

Follow these best practices when approaching a VB6 to .NET Core migration:

Create a Detailed Migration Plan

Analyze all migration costs, risks, timelines, constraints, dependencies, and business expectations. Document objectives, assumptions, and success criteria in a formal plan.

Prioritize Business Value

Sequence the migration to modernize applications that deliver the most business value first. Defer peripheral apps to later phases.

Validate Converted Code

Use automated unit, integration, load, and user acceptance testing to validate apps behave correctly after migration.

Provide Developer Training

Invest in training the teams in .NET Core features, structures, design patterns, testing, and security systems.

Upgrade Supporting Systems

Upgrade build/deploy pipelines, monitoring, operations, and related infrastructure as well as the applications.

Staying in line with the best practices of structured migration supports business needs while also keeping modernization goals in check and framing the work done from the long-term perspective.

Conclusion

Porting business-critical VB6 applications to more sustainable modern environments, such as .NET Core, has many advantages but also many problems. Managers need to allocate sufficient time, funds, and planning for the process to be effective.

Although a certain amount of manual redevelopment is necessary, the use of automated translation tools along with interoperability solutions can minimize initial costs and associated risks. Approximating and accurately assessing developers also facilitates the process, and rough testing and thorough developer training also ease the process.