Version Compatibility

Visual Basic's Version Compatibility feature is a way of enhancing your components while maintaining backward compatibility with programs that were compiled using earlier versions. The Version Compatibility box, located on the Component tab of the Project Properties dialog box, contains three options:

• No Compatibility: Each time you compile the component, new type library information is generated, including new class IDs and new interface IDs. There is no relation between versions of a component, and programs compiled to use one version cannot use subsequent versions.
• Project Compatibility: Each time you compile the component the type library identifier is kept, so that your test projects can maintain their references to the component project. All class IDs from the previous version are maintained; interface IDs are changed only for classes that are no longer binary-compatible with their earlier counterparts.
• Binary Compatibility: When you compile the project, if any binary-incompatible changes are detected you will be presented with a warning dialog. If you choose to accept the warning, the component will retain the type library identifier and the class IDs. Interface IDs are changed only for classes that are no longer binary-compatible. This is the same behavior as Project Compatibility.

If, however, you choose to ignore the warning, the component will also maintain the interface IDs. This option is only available when the compiler determines that the change was in the procedure ID or signature of a method.