Chapter 12: From COM to COM+
For about 10 years, starting soon after the release of Windows 3.0, Microsoft has been promising that its operating system and its API would be based on a real object model instead of functions. According to the speculations, Windows 95 (and later Windows 2000) should have been based on this revolutionary approach. Nothing like this happened, but Microsoft kept pushing COM (Component Object Model), built the Windows 95 shell on top of it, pushed applications integration with COM and derivative technologies (such as Automation), and reached the peak by introducing COM+ with Windows 2000.
Now, soon after the release of the complete foundation required for high-level COM programming, Microsoft has decided to switch to a new core technology, part of the .NET initiative. My impression is that COM wasn't really suited for the integration of fine-grained objects, although it succeeded in providing an architecture for integrating applications or large objects.
In this chapter, you'll build your first COM object; I'll stick to the basic elements to let you understand the role of this technology without delving heavily into the details. We'll continue by discussing Automation and the role of type libraries, and you'll see how to work with Delphi data types in Automation servers and clients.
In the final part of the chapter, we'll explore the use of embedded objects, with the OleContainer component, and the development of ActiveX controls. I'll also introduce stateless COM (MTS and COM+) technologies and a few other advanced ideas including the .NET integration support offered by Delphi 7.
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