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    Creating XPCOM components

    This guide is about Gecko, and about creating XPCOM components for Gecko-based applications. Though the emphasis is on the practical steps you take to make your C++ code into a component that can be used in Gecko, we hope that these steps will also give us an occasion to discuss all of the tools, techniques, and technologies that make up XPCOM. Accordingly, the book is arranged so that you can follow along and create your own components or learn about different XPCOM topics individually, as in a reference work. For example, the introduction includes a discussion of components and what they are, and the first chapter - in which you compile the basic code and register it with Mozilla - prompts a discussion of the relationship between components and modules, of XPCOM interfaces, and of the registration process in general.

    Note: In general, you should try to avoid having to create XPCOM components. Add-ons should try to use the new Add-on SDK as much as possible; however, there may be cases when it's unavoidable.

    Note:This article describes a method that uses xpidl but you should use webidl instead.


    Who Should Read This Book
    Organization of the Tutorial
    Following Along with the Examples

    An Overview of XPCOM

    The XPCOM Solution
    Interfaces and Encapsulation
    The nsISupports Base Interface
    XPCOM Identifiers
    Contract ID
    XPIDL and Type Libraries
    XPCOM Services
    XPCOM Types
    Method Types
    Reference Counting
    Status Codes
    Variable Mappings
    Common XPCOM Error Codes

    Using XPCOM Components

    Component Examples
    Cookie Manager
    The WebBrowserFind Component
    The WebLock Component
    Component Use in Mozilla
    Finding Mozilla Components
    Using XPCOM Components in Your Cpp
    XPConnect: Using XPCOM Components From Script

    Component Internals

    Creating Components in Cpp
    XPCOM Initialization
    XPCOM Registry Manifests
    Registration Methods in XPCOM
    The Shutdown Process
    Three Parts of a XPCOM Component Library
    XPCOM Glue
    The Glue Library
    XPCOM String Classes

    Creating the Component Code

    What We'll Be Working On
    Component Registration
    The regxpcom Program
    Registration Alternatives
    Overview of the WebLock Module Source
    Digging In: Required Includes and Constants
    Identifiers in XPCOM
    Coding for the Registration Process
    The Registration Methods
    Creating an Instance of Your Component

    Using XPCOM Utilities to Make Things Easier

    XPCOM Macros
    Generic XPCOM Module Macros
    Common Implementation Macros
    Declaration Macros
    String Classes in XPCOM
    Using Strings
    nsEmbedString and nsEmbedCString
    Smart Pointers

    Starting WebLock

    Getting Called at Startup
    Registering for Notifications
    Getting Access to the Category Manager
    Providing Access to WebLock
    Creating the WebLock Programming Interface
    Defining the WebLock Interface in XPIDL
    The XPIDL Syntax
    Scriptable Interfaces
    Subclassing nsISupports
    The Web Locking Interface
    Implementing WebLock
    Declaration Macros
    Representing Return Values in XPCOM
    XPIDL Code Generation
    Getting the WebLock Service from a Client
    Implementing the iWebLock Interface
    The Directory Service
    Modifying Paths with nsIFile
    Manipulating Files with nsIFile
    Using nsILocalFile for Reading Data
    Processing the White List Data
    iWebLock Method By Method
    Lock and Unlock

    Finishing the Component

    Using Frozen Interfaces
    Copying Interfaces Into Your Build Environment
    Implementing the nsIContentPolicy Interface
    Receiving Notifications
    Implementing the nsIContentPolicy
    Uniform Resource Locators
    Checking the White List
    Creating nsIURI Objects

    Building the WebLock UI

    User Interface Package List
    Client Code Overview
    The XUL Document
    The Locking UI
    Site Adding UI
    Overlaying New User Interface Into Mozilla
    Other Resources
    Image Resources

    Packaging WebLock

    Component Installation Overview
    Archiving Resources
    The WebLock Installation Script
    The WebLock Trigger Script
    Distributing Your Component

    Appendix A - Setting up the Gecko SDK

    Downloading and Setting the SDK
    Building a Microsoft Visual Cpp Project
    Creating a New Project
    Adding the Gecko SDK to the Project Settings
    Building a Windows Project
    A Makefile for Unix

    Appendix B - Resources

    WebLock Resources
    Gecko Resources
    XPCOM Resources
    General Development Resources

    Copyright (c) 2003 by Doug Turner and Ian Oeschger. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.02 or later. Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.

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