Type Libraries and ActiveX Objects

You must create a type library for each set of exposed objects. Because VTBL references are bound at compile time, exposed objects that support VTBL binding must be described in a type library.

Type libraries provide these important benefits:

• Type checking can be performed at compile time. This may help developers of ActiveX clients to write fast, correct code to access objects.

• You can describe an interface with type information and implement IDispatch::Invoke for the interface using a single call to DispInvoke.

• Visual Basic applications can create objects with specific interface types, rather than the generic Object type, to take advantage of early binding.

• ActiveX clients that do not support VTBLs can read and cache DISPIDs at compile time, improving run-time performance.

• Type browsers can scan the library, allowing others to see the characteristics of objects.

• The RegisterTypeLib function can be used to register exposed objects in the registration database.

• The UnRegisterTypeLib function can be used to completely uninstall an application from the system registry.

• Local server access is improved because Automation uses information from the type library to package the parameters that are passed to an object in another process.

In this section

Topic	Description
Creating a Type Library	Demonstrates how to create a type library.
Building a Type Library	Demonstrates how to build a type library.
Registering a Type Library	Demonstrates how to register a type library.
Returning an Error	ActiveX objects typically return rich contextual error information, which includes an error number, a description of the error, and the path of a Help file that supplies more information.