Intro to COM

What is it and what can it do for me?

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.

OK, What are Components?

• Components are big brother of Classes. Component = Object

• Interface = Function Set of that Object• Properties = Member Variables

– (all Properties are actually get & put calls)

• Methods = Functions

• BONUS: Components can have more than one interface.

What makes up a Component?

• Implementation object• Interface object(s)

IFooExIFoo Implementation

Object

IUnknown

Components are well-encapsulated objects

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

Where do components live?

• In-Process servers (.dll)• Out-of-Process servers (.exe)• Remote servers (.exe)• ActiveX (.ocx)

Using Components

• Rapid Application Development• Seamless application updates• Build great apps without reinventing the wheel• Interface different systems with ease

• Examples: Serial port communications, Scanner image capture, Image archive systems, internet server interaction (CDDB)

What languages can I use?

• C++, Java, Visual Basic and VB Script (IIS)

• ActiveX technology, Use MS ATL (VC++)

• Component creation

• Component use in applications

Why should you learn COM?

• 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.

Parallel Programming

• Three main types of applications:– CPU intensive

• graphics rendering• BFA

– Resource Specific• DCOM lets you do this seamlessly

– Highly connected• custom data, application structures • hybrid memory models

Cradle - Traveling Salesman

Traveling Salesman - 13 Ponts

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16 sec

Traveling Salesman - 17 Points(43,680 times the calculation)

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197 days

3.5 Days

Life 3D

Life3D face relationships

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Symera Viewer

Clustering Scenarios

Tight Coupling Loose Coupling

Life3D Class Conversion

CMainWindow CFaceWindow

CCubeFace(interface)

CFace(implementation)

CSymObj CSymObjRef

Original classes

New classes

Symera base classes

CCubeFace

CSymObj

User Interface Distributed Object

Recommended Reading

• Dr. GUI articles on COM - a MUST READ• Essential COM by Don Box• Inside COM & Inside Distributed COM (MS Press)• ActiveX/COM Control Programming (WROX Press)

• For the complete history and theory, read:– Inside OLE (MS Press)