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Effective Visual Basic: How to Improve Your VB/COM+ Applications

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Effective Visual Basic: How to Improve Your VB/COM+ Applications

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  • Copyright 2001
  • Edition: 1st
  • Premium Website
  • ISBN-10: 0-201-70476-5
  • ISBN-13: 978-0-201-70476-1

Featuring nearly fifty rules for best practice, EFFECTIVE VISUAL BASIC gives the working programmer concrete guidelines for designing better systems and writing better code. Whether the focus is COM, databases, or distributed systems using MTS and COM+, this book offers proven, timeless solutions derived from the authors’ years of experience consulting and training in the VB arena.

EFFECTIVE VISUAL BASIC addresses general practices, from defensive programming to error handling and object-oriented design. In addition, it covers the critical issues in working with COM: interfaces, compatibility, and class design. Rules for building multi-tier applications are followed by a section on best practices for programming the Web. This book also addresses databases and effective data access, among the most important uses of VB.

Highlights include:

  • Sound programming practices and object-oriented design principles, as applicable in VB.NET as in VB6
  • Writing code that runs correctly in both MTS and COM+ environments
  • Improving scalability by not necessarily configuring all your components
  • Using XML, IIS, and ASP in Web applications
  • Designing classes for efficient database access

The product of a wealth of practical experience, EFFECTIVE VISUAL BASIC enables readers to advance their skills and become more effective software developers.



0201704765B04062001

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Designing, Building, and Working with COM-Based Components

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Table of Contents



1. Shifting from Liberal Arts to Software Engineering.

Maximize the Potential of VB's Compile-Time Type Checking.

Make Assumptions Explicit Via Debug.Assert.

Consider #If When Compile-Time Conditions Differ.

Raise Errors to Signal Exceptional Conditions.

Trap Locally, Act Globally: Effective Error Handling.

Know the Difference Between Type and Class.

Embrace Good Object-Oriented Design, Not Just VB.

Prefer UDTs Over Classes for Value Types.

Automate Mundane Tasks.



2. Designing, Building, and Working with COM-Based Components.

Think in Terms of Interfaces.

Use Custom Interfaces.

Define Custom Interfaces Separately, Preferably Using IDL.

Avoid the Limitations of Class-Based Events with Custom Call-Backs.

Be Deliberate about Maintaining Compatibility.

Choose the Right COM Activation Technique.

Beware of Class_Terminate.

Model in Terms of Scenarios Instead of Entities.

Avoid ActiveX EXEs Except for Simple, Small-Scale Needs.



3. MTS, COM+, and VB—The Middle Tier.

Understand the Design of MTS and COM+.

Don't Use Singletons in MTS and COM+.

Know When to Use New versus CreateObject versus GetObjectContext.CreateInstance.

Understand the Real Motivation for SetComplete.

Consider an Auto-Abort Style with Transactions.

Don't Reinvent the DBMS.

Don't Feel Obligated to Configure All Your Components.

Avoid Compiling Things into DLLs that You'll Later Regret.

Best Practices for Porting MTS Code into COM+.

Best Practices for Writing Code that Runs on MTS and COM+.



4. The Web and VB.

Understand the IIS Architecture.

Manage Application State to Maximize Efficiency.

Manage Session State to Maximize Scalability.

Understand the Differences Between DCOM and HTTP.

Write COM Components for Scripting Environments (like ASP).

Understand How Your COM Objects Interact with ASP.

Use XML Instead of Proprietary Data Formats.

Be Deliberate about Presentation vs. Business Logic.

Use XSLT to Move from Data to Presentation.



5. Effective Data Access from VB.

Efficiency Basics: Roundtrips, SQL Statements, and Providers.

Don't Over-Encapsulate Data Access.

Never Hold Database Connections as Data Members.

Deadlock is Common; Develop Defensively.

Use Firehose Cursors whenever Possible.</LI>

Make the Right Data Searching Decision (Avoid SelectSingleNode Abuse).



Index.

Preface

Visual Basic (VB) has become the most popular programming language in the United States. It is a large language and a complex product. Yet the ease with which it builds graphical user interfaces, accesses databases, and supports the Component Object Model (COM) is impressive.

This book is written by VB programmers for VB programmers. We assume you have been working with VB for quite some time and, if you’re lucky, in a variety of ways: building front ends, reading databases, generating Web pages, programming COM objects. The goal of this book is to summarize a number of effective VB techniques that we have learned—and put into practice—over the years. This book has something for everyone, from general practices and COM-based components to COM+ and distributed applications. The wider your exposure to VB and the Windows Distributed Internet Application Architecture (DNA), the more applicable you’ll find the techniques.

We follow the style of other books in the DevelopMentor series, in that each technique stands alone as an independent item ready for application. We try our best to describe each item as concisely as possible, and to let you read the book in any order you like. In a few cases, however, one rule leads quite naturally to another and thus should be read in that order; we’ll point these dependencies out to you.

If we’ve done our job, then reading this book—and taking its ideas to heart—will make you a more effective VB programmer. It will also make you a better practitioner because your skills will improve in other areas as well, such as object-oriented design, MTS, databases, and the Web.

Acknowledgments

We all work for a developer services company called DevelopMentor. It’s how we met, and how we keep abreast of the technology. It’s also a fantastic place to spend one’s working hours, and we owe this book (and much more) to our friends and coworkers at DM. If you ever want to see what DevelopMentor is all about, attend one of our Guerilla events—and be sure not to miss out on Thursday night. By the way, it’s not just the employees that make DM; it’s also the students and their energy. Thank you.

We also thank Gary Clarke for his sustained effort in getting this project off the ground and flying. We owe a great deal, as well, to Kristin Erickson (and her coworkers!) at Addison-Wesley for her tireless work behind the scenes, bringing this book to completion.

The anonymous reviewers did an excellent job, and we thank them for their hard work under a tight schedule. The book is much better as a result.

Finally, we’d like to thank our families for their boundless support and understanding during our late nights of reading, researching, writing, and reinstalling Windows.



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Index

A Abstraction, 42, 43–44, 46
Access permissions, checking, 170
ACID rules, 142, 154, 155
Activation, COM, 91, 99–110
CreateObject function, 99, 103–105
    GetObjectContext.CreateInstance and Server.CreateObject, 99, 100, 106–107
    GetObject function, 99, 105–106
    New operator, 102–103
    performance considerations, 107–110
    types of, 107–108, 109, 118–119
Active Template Library (ATL), 143
ActiveX EXEs, 118–122
Activities in MTS/COM+, 124, 126, 127–128, 131
ADO disconnected recordset, 297
ADO objects, 136–137
ADO Recordset, 231–232, 235, 273, 288
    disconnected, 297
Advanced Data Tablegram format (ADTG), 235
Apartment–threaded object, 221
    Application variable and, 223–224
    Session variable and, 222–223
API calls, 30
Application object. See ASP Application object
Application state management, 184–194
    ASP Application object, 191–193
    BAS module data and, 185–188
    SPM and, 188–191
    weighing options for, 193–194
Arguments
    in conditional compilation, 15–17, 19
    in scripts, 58
ASP, 150, 175, 185
    eliminating from distributed application, 206–208
    interaction with COM, 218–227
    intrinsic objects, 219–220
        benefits of, 225–226
        disadvantages of, 226–227
    presentation layer–business logic layer separation and, 236–243
        MTS components and, 238–239
        WebClasses and, 240–243
    thread–pooling scheme, 223
    threads in, 186
ASP.dll, 175
ASP Application object, 153–154, 220
    apartment–threaded object and, 223–224
    caching using, 191–193
ASP page, object creation from, 137
ASP Session object, 194–195, 219
AspTrackThreadingModel property, 224
Assignment of class versus type, 38, 39–40
Assumptions, explicit, 8–14
ATL (Active Template Library), 143
Atomicity, issue of, 154
Auto–abort style with transactions, 146–150
Automating mundane tasks, 53–60
    with nmake, 53–56
    with Windows Scripting Host (WSH),
56–60
B Base client, 130
BAS modules, 122, 150
    caching data in, 185–188
    variables, 187–188
Batch files, 53
Batch SQL statement, 261–262
Binary Compatibility setting, 95–96, 97
Binding, client–object, 107
Binding mechanisms, client–object, 100–101
Brittle–code problem, 248–249
Browser, 237
Builds, debug versus release, 15–16
Business logic layer–presentation layer separation, 236–243
    MTS components and, 238–239
    WebClasses and, 240–243
ByRef, 36, 37, 40
ByVal, 36, 37, 40
C C++, 41
Caching, 151, 156
    of durable state web application, 184–194
        ASP Application object, 191–193
        BAS module data and, 185–188
        SPM and, 188–191
        weighing options for, 193–194
    in–memory, 150–151
Callbacks, custom, 83–90
Class(es)
    accessing, 66
    custom interfaces and evolution of, 67–69
    groups of, 48
    real–world entities modeled by, 42–43
    type versus, 35–41
    value types and, 49–52
Class–based events, 83–86
Class–based references, 67
Class_Initialize, 43
Class_Terminate, 43, 111–114
Cleanup, 111–114
Client(s)
    accidental DLL installation on, 170–171
    base, 130
    compiled, 93–96
    object binding by, 100–101
    scripting, 92–93
    storing session information on, 196–201
        via cookies, 197–198
        in database, 201–202
        in header, 197–198
        in hidden form fields, 200–201
        with QueryString variables, 199–200
Close methods, 111–112
CLSIDs, 91
Coclass (COM class) definitions, 81
CoCreateInstance, 164
CoCreateInstanceEx, 164
COM+, 119, 123–172
    activities in, 124, 126, 127–128
    Auto–Abort style with transactions, 146–150
    coding practices for, 169–172
    components configuration issues, 157–158
    context in, 157
    DBMS issues, 150–156
    design of, 124–127
    DLL issues, 159–164
    object creation in, 129–140
    porting MTS to, 164–169
        declarative security checks and, 167
        GetObjectContext.CreateInstance and, 164–165
        MSI and, 168–169
        ObjectConstruct string and,
166–167
        RefreshComponents command and, 167–168
        SafeRef and, 165
        secondary object errors and, 165–166
    SetComplete, 140–146
    singletons in, 127–129, 132
    synchronization in, 125–126
    threads in, 186
    transactional methods in, 141–142
    transaction infrastructure in, 282–283
    Windows 2000 and, 138–139, 149–150
COM. See also DCOM
    activation, 91, 99–110
        CreateObject function, 99, 103–105
        GetObjectContext.CreateInstance and Server.CreateObject, 99, 100, 106–107
        GetObject function, 99, 105–106
        New operator, 102–103
   &nb

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