OLE Custom Interfaces

As an OLE developer, you implement and use objects that are based on the Component Object Model (COM). COM interfaces specify a contract between the interface implementor and its user. The contract applies to every COM object that supports that interface.

OLE provides a standard set of interfaces, but these OLE-provided interfaces may not be perfectly suited to your needs. Through custom interfaces, you can create new ones tailored to fulfill the specific needs of your application. Custom interfaces are extensions to the COM standard; they let you extend the standard behavior and still take advantage of the services provided by the base interface. Like all COM interfaces, custom interfaces derive from the IUnknown interface and must contain the three methods of IUnknown. Otherwise, they can support a wide range of methods and parameters. (Note that, currently, custom interfaces cannot include asynchronous methods. Asynchronous methods may be supported in future versions of OLE.)

Once the interface is written, anyone can use it. Calls to methods in COM interfaces can cross process boundaries as long as both processes are running on the same machine.

This appendix introduces custom interfaces and explains how to implement them. OLE experience is a prerequisite, as is a basic knowledge of RPC. For more information about OLE and COM technology, see the OLE Reference Guide and the other parts of this OLE Programmer's Guide. Refer to the RPC Programmer's Guide and Reference for information about the RPC programming environment.

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