COM Programming by Example: Using MFC, ActiveX, ATL, ADO, and COM+ (with CD-ROM

385 Pages·2000·4.41 MB·English

by  John E. Swanke

COM Programming
by Example
Using MFC, ActiveX, ATL, ADO, and
COM+
John E. Swanke
R&D Books
Lawrence, Kansas 66046
R&D Books
CMP Media, Inc.
1601 W. 23rd Street, Suite 200
Lawrence, KS 66046
USA
Designations used by companies to distinguish their products are often claimed as trade-
marks. In all instances where R&D is aware of a trademark claim, the product name
appears in initial capital letters, in all capital letters, or in accordance with the vendor’s
capitalization preference. Readers should contact the appropriate companies for more
complete information on trademarks and trademark registrations. All trademarks and
registered trademarks in this book are the property of their respective holders.
Copyright © 2000 by John Swanke, except where noted otherwise. Published by R&D
Books, CMP Media, Inc. All rights reserved. Printed in the United States of America. No
part of this publication may be reproduced or distributed in any form or by any means, or
stored in a database or retrieval system, without the prior written permission of the pub-
lisher; with the exception that the program listings may be entered, stored, and executed in
a computer system, but they may not be reproduced for publication.
The programs in this book are presented for instructional value. The programs have been
carefully tested, but are not guaranteed for any particular purpose. The publisher does
not offer any warranties and does not guarantee the accuracy, adequacy, or completeness
of any information herein and is not responsible for any errors or omissions. The pub-
lisher assumes no liability for damages resulting from the use of the information in this
book or for any infringement of the intellectual property rights of third parties that
would result from the use of this information.
Cover art created by Robert Ward.
Distributed in the U.S. and Canada by:
Publishers Group West
1700 Fourth Street
Berkeley, CA 94710
1-800-788-3123
ISBN: 1-929629-03-6
R&D Developer Series
For My Wife, Cathy Krinitsky,
My Great Woman
And for Paul Swanke,
A Friend Indeed
This Page Intentionally Left Blank
Acknowledgments
I’d like to thank everyone who worked on this book, directly or indirectly:
Berney Williams for believing in this format, Paul Temme for his marketing
acumen, and Michelle Dowdy and Kristi McAlister for making me sound
like Hemingway (if he was a geek) and pulling it all together. I’d also like to
thank Mike Wallace for making sure this book is more fact then fiction —
and of course for keeping the manuscript out of Morley’s hands.
Learning a subject is never done in a vacuum. I’d like to thank the people
I learned COM with: my brother Paul, John Creaser, and Bob Otterberg,
I’d also like to acknowledge the entire gang at NeuVis, Inc. for creating
an enterprise that’s doing some pretty remarkable things with COM. Neu-
Vis includes Rajiv Uppal, Jim Farrell, Devang Parikh, Jose Bescheider, Ritu
Gupta, Tony “EJB” Tao, everybody who would be disappointed not to be
mentioned here, and the genius behind NeuVis, Arun Gupta.
v
This Page Intentionally Left Blank
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xix
What’s In Store. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Section I: COM Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Section II: COM Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xx
About the CD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xx
About the SampleWizard. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xx
Section I COM Basics..................................1
COM Objects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
COM Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Other COM Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
COM+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Chapter 1 COM Objects. . . . . . . . . . . . . . . . . . . . . . 3
What is COM?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Why Was COM Developed?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
What are the Other Uses of COM?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
How Does COM Work?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
How Do You Create a COM Object Using C++?. . . . . . . . . . . . . . . . . . . .8
How Do You Communicate with Your COM Object Using C++? . . . . . .12
Cautions and Warnings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
How Do You Destroy Your COM Object?. . . . . . . . . . . . . . . . . . . . . . . .15
How Do You Create a COM Object Using #import and Smart
Pointers?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
vii
viii Table of Contents
How Do You Write a COM Object Using C++?. . . . . . . . . . . . . . . . . . . 18
The IDL File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
IUnknown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Other COM Object Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Writing a COM Object in Straight C++ . . . . . . . . . . . . . . . . . . . . . . . . . 24
How Do You Write a COM Object Using MFC?. . . . . . . . . . . . . . . . . . 25
Custom Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
How Do You Write a COM Object Using ATL? . . . . . . . . . . . . . . . . . . 27
So How Do You Create a COM Object with Visual Basic? . . . . . . . . . . 27
So How Do You Create a COM Object with Visual J++?. . . . . . . . . . . . 28
What’s the Service Control Manager?. . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter 2 COM Communication. . . . . . . . . . . . . . 31
How Do COM Objects Communicate? . . . . . . . . . . . . . . . . . . . . . . . . . 31
Basic IDL File Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Early-Binding Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Late-Binding Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Dual Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
The VTBL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Type Library Declaration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Simple Argument Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Structures and COM Classes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Encapsulated Unions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Memory Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Visual Basic Argument Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
BSTRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
SafeArrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Variants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Reverse Communication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Connection Points and Sinks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Early-Binding Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Late-Binding Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
ActiveX Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Table of Contents ix
Chapter 3 Other COM Issues. . . . . . . . . . . . . . . . . 53
Encapsulation and Aggregation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Aggregation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
Security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
Activation Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
Object Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
CoInitializeSecurity(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
Licensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
Multitasking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Thread Safety Primer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
COM Thread Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
Automatic COM Thread Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
Activating Thread Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Synchronization Loopholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Designing Your In-Process COM Server . . . . . . . . . . . . . . . . . . . . . .70
Designing Your Out-of-Process COM Server. . . . . . . . . . . . . . . . . . .71
Apartments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Chapter 4 COM+ . . . . . . . . . . . . . . . . . . . . . . . . . . 75
The Evolution of Client/Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
The Evolution of COM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
DLL Surrogates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
Writing Your Own DLL Surrogate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Microsoft Transaction Server (MTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Stateless Programming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
IObjectContext. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
Thread Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Writing Your MTS Compliant COM Server . . . . . . . . . . . . . . . . . . .85
Registering Your MTS Object. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
What is COM+? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Just-in-Time Activation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
Object Pooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89
Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
A New Threading Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91
Event Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
Queued Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
Security at the Method Level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
Other Minor Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98