1. Intro to COM What is it and how do I use it?

2. Objectives Teach the fundamentals of COM. Understand the reason for using it. Learn to make a simple in-process server.

3. COM Defined COM (Component Object Model) and DCOM (Distributed COM) are a set of binary and network standards for the modeling of objects and their communications.

4. What does it do? It allows for “Plug and Play” software. Helps to create distributed systems transparently.

5. Why should you learn COM? Flexibility: can be used from and written in all popular languages. Saves tremendous time (after the initial learning curve) Use of existing objects Object Reuse: C++ tried to address this issue, but just made it easy to reuse source code. So you can use DCOM.

6. Why should you learn COM? Rapid Application Development Seamless application updates Build great apps without reinventing the wheel Interface different systems with ease

7. Component Hierarchy Components are made up of objects Objects are made up of interfaces Interfaces are made up of member functions

8. What makes an object? Objects support object-oriented principles: 4encapsulation 4polymorphism 4inheritance? Conceptual in nature Known only through interfaces ObjectInterfaces

9. What makes an object? Clients can interact with any object without knowing which object with which it interacts Object 1 Object 2 Client

10. The Specifics

11. Identifiers GUID (globally unique identifiers) –are stored in 16-byte (128 bit) structures CLSID (class identifier GUID) IID (interface identifier GUID) IUnknown QueryInterface –Returns a pointer to requested Interface AddRef –Increases the RefCount Release –Decreases the RefCount

12. Interfaces An interface is a set of similar methods –Analogous to a C++ class Binary level, not source code level Indentified by an Interface Identifier (IID) interface ISquirrel : IUnknown { HRESULT EatNuts(); HRESULT ClimbTree(); HRESULT RunAway(); };

13. IUnknown Base interface Polymorhic to all other interfaces Implements reference counting All other interfaces are retrieved through IUnknown interface IUnknown { ULONG AddRef(); ULONG Release(); HRESULT QueryInterface(REFIID iid, void **ppObject); };

14. Accessing Objects CoCreateInstance Based on a class ID (CLSID) Specify requested interface Object can be anywhere STDAPI CoCreateInstance( REFCLSID rlcsid, LPUNKNOWN pUnkOuter, DWORD dwClsContext, REFIID riid, LPVOID *ppv );

15. Where do components live? In-Process servers (.dll) Out-of-Process servers (.exe) Remote servers (.exe) ActiveX (.ocx)

16. Uses ActiveX DCOM DirectX Automation OLE etc.

17. Recommended Reading The definitive beginner’s guide to COM: –Inside COM by Dale Rogerson A great online tutorial that summarizes much of Inside COM: –http://beta.develop.com/comtutorial For the complete history and theory: –Inside OLE by Kraig Brockschmidt