Migrating Applications from VB 6.0 to VB .NET

Introduction

Microsoft Visual Basic has had many evolutions since its original release, Visual Basic 1.0. The release of Visual Basic .NET is the biggest evolution yet. The language has been redesigned to take advantage of the .NET Framework. By leveraging the features that the .NET Framework provides, Visual Basic supports language features such as code inheritance, visual forms inheritance, and multi-threading. The object model is more extensive than earlier versions, and Visual Basic .NET totally integrates with the .NET Framework. Therefore, interaction between components written in other .NET languages is very efficient.

Benefits Reaped:

• Visual Basic .NET is the next version of Visual Basic. Rather than simply adding some new features to Visual Basic 6.0, Microsoft has reengineered the product to make it easier than ever before to write distributed applications such as Web and enterprise n-tier systems. Visual Basic .NET has two new forms packages (Windows Forms and Web Forms); a new version of ADO for accessing disconnected data sources; and streamlined language, removing legacy keywords, improving type safety, and exposing low-level constructs that advanced developers require.

• These new features open new doors for the Visual Basic developer: With Web Forms and ADO .NET, you now can rapidly develop scalable Web sites; with inheritance, the language now truly supports object-oriented programming; Windows Forms natively supports accessibility and visual inheritance; and deploying your applications is now as simple as copying your executables and components from directory to directory.

• Visual Basic .NET is now fully integrated with the other Microsoft Visual Studio .NET languages. Not only can you develop application components in different programming languages, your classes also can now inherit from classes written in other languages using cross-language inheritance. With the unified debugger, you can now debug multiple language applications, irrespective of whether they are running locally or on remote computers. Finally, whatever language you use, the Microsoft .NET Framework provides a rich set of APIs for Microsoft Windows® and the Internet.

• There were two options to consider when designing Visual Basic .NET—retrofit the existing code base to run on top of the .NET Framework, or build from the ground up, taking full advantage of the platform. To deliver the features most requested by customers (for example, inheritance and threading), to provide full and uninhibited access to the platform, and to ensure that Visual Basic moves forward into the next generation of Web applications, the right decision was to build from the ground up on the new platform. For example, many of the new features found in Windows Forms could have been added to the existing code base as new controls or more properties. However, this would have been at the cost of all the other great features inherent to Windows Forms, such as security and visual inheritance.

• One of Microsoft's major goals was to ensure Visual Basic code could fully interoperate with code written in other languages, such as Microsoft Visual C# or Microsoft Visual C++, and enable the Visual Basic developer to harness the power of the .NET Framework simply, without resorting to the programming workarounds traditionally required to make Windows APIs work. Visual Basic now has the same variable types, arrays, user-defined types, classes, and interfaces as Visual C++ and any other language that targets the Common Language Runtime; however, we had to remove some features, such as fixed-length strings and non-zero based arrays from the language.

• Visual Basic is now a true object-oriented language; some unintuitive and inconsistent features such as GoSub/Return and DefInt have been removed from the language.

• The result is a re-energized Visual Basic, which will continue to be the most productive tool for creating Windows-based applications, and is now positioned to be the best tool for creating the next-generation Web sites.