source: branches/4.5.1/doc/src/qthelp.qdoc@ 1055

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/*!
    \module QtHelp
    \title QtHelp Module
    \contentspage Qt's Modules
    \previouspage QtUiTools
    \nextpage QtAssistant
    \ingroup modules

    \brief The QtHelp module provides classes for integrating
    online documentation in applications.

    To include the definitions of the module's classes, use the
    following directive:

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 0

    To link against the module, add this line to your \l qmake \c
    .pro file:

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 1

    \note These classes are part of the \l{Open Source Versions of Qt} and
    \l{Qt Commercial Editions}{Qt Full Framework Edition} for commercial
    users.

    \section1 Topics

    \tableofcontents

    \section1 Overview
    The Qt help system includes tools for generating and viewing
    Qt help files. In addition it provides classes for accessing
    help contents programatically to be able to integrate online
    help into Qt applications.

    The actual help data, meaning the table of contents, index
    keywords or html documents, is contained in Qt compressed help
    files. So, one such a help file represents usually one manual
    or documentation set. Since most products are more comprehensive
    and consist of a number of tools, one manual is rarely enough.
    Instead, more manuals which should be accessible at the same
    time, exist. Ideally, it should also be possible to reference
    certain points of interest of one manual to another.
    Therefore, the Qt help system operates on help collection files
    which include any number of compressed help files.

    However, having collection files to merge many documentation
    sets may lead to some problems. For example, one index keyword
    may be defined in different documentations. So, when only seeing
    it in the index and activating it, you cannot be sure that
    the expected documentation will be shown. Therefore, the Qt
    help system offers the possibiltiy to filter the help contents
    after certain attributes. This requires however, that the
    attributes have been assigned to the help contents before the
    generation of the compressed help file.

    As already mentioned, the Qt compressed help file contains all
    data, so there is no need any longer to ship all single html 
    files. Instead, only the compressed help file and optionally the
    collection file has to be distributed. The collection file is
    optional since any existing collection file, e.g. from an older
    release could be used.

    So, in general, there are four files interacting with the help
    system, two used for generating Qt help and two meant for
    distribution:

    \table
        \header
            \o Name
            \o Extension
            \o Brief Description
        \row
            \o \l {Qt Help Project}
            \o .qhp
            \o The input file for the help generator consisting of the table
               of contents, indices and references to the actual documentation
               files (*.html); it also defines a unique namespace for the
               documentation.

        \row
            \o Qt Compressed Help
            \o .qch
            \o The output file of the help generator. This binary file contains
               all information specified in the help project file along with all
               compressed documentation files.

        \row
            \o \l {Qt Help Collection Project}
            \o .qhcp
            \o The input file for the help collection generator. It contains
               references to compressed help files which should be included in
               the collection; it also may contain other information for
               customizing Qt Assistant.

        \row
            \o Qt Help Collection
            \o .qhc
            \o The output of the help collection generator. This is the file
               QHelpEngine operates on. It contains references to any number of
               compressed help files as well as additional information, such as
               custom filters.
    \endtable

    \section1 Generating Qt Help

    Building help files for the Qt help system assumes that the html
    documentation files already exist, i.e. the Qt help system does
    not offer the possibility to create html files like e.g. Doxygen.

    Once the html documentents are in place, a \l {Qt Help Project} file
    has to be created. After specifying all relevant information in
    this file, it needs to be compiled by calling:

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 2

    The file 'doc.qch' contains then all html files in compressed
    form along with the table of contents and index keywords. To
    test if the generated file is correct, open Qt Assistant and
    install the file via the Settings|Documentation page.

    \target Qt Help Collection Project
    \section2 Creating a Qt Help Collection

    The first step is to create a Qt Help Collection Project file.
    Since a Qt help collection stores primarily references to
    compressed help files, the project 'mycollection.qhcp' file
    looks unsurprisingly simple:

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 3

    For actually creating the collection file call:

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 4

    Instead of running two tools, one for generating the compressed
    help and one for generating the collection file, it is also
    possible to just run the qcollectiongenerator tool with a
    slightly modified project file instructing the generator to
    create the compressed help first.

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 5

    Of course, it is possible to specify more than one file in the
    'generate' or 'register' section, so any number of compressed
    help files can be generated and registered in one go.

    \section1 Using Qt Help

    Accessing the help contents can be done in two ways: Using Qt
    Assistant as documentation browser or using the QHelpEngine
    API for embedding the help contents directly in an application.

    \section2 Using Qt Assistant

    \QA operates on a collection file which can be specified
    before start up. If no collection file is given, a default one
    will be created and used. In either case, it is possible to
    register any Qt compressed help file and access the help contents.

    When using Assistant as the help browser for an application, it
    would be desirable that it can be customized to fit better to the
    application and doesn't look like an independent, standalone
    help browser. To achieve this, several additional properties can
    be set in an Qt help collection file, to change e.g. the title
    or application icon of Qt Assistant. For more information on
    this topic have a look at the \l{assistant-manual.html}
    {Qt Assistant manual}.

    \section2 Using QHelpEngine API

    Instead of showing the help in an external application like the
    Qt Assistant, it is also possible to embed the online help in 
    the application. The contents can then be retrieved via the
    QHelpEngine class and can be displayed in nearly any form.
    Showing it in a QTextBrowser is probably the most common way, but
    embedding it in What's This help is also perfectly possible.

    Retrieving help data from the file engine does not involve a
    lot of code. The first step is to create an instance of the
    help engine. Then we ask the engine for the links assigned to
    the identifier, in this case "MyDialog::ChangeButton". If a link
    was found, meaning at least one help document exists to this topic,
    we get the actual help contents by calling fileData() and display
    the document to the user.

    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 6

    For further information on how to use the API, have a look at
    the QHelpEngine class reference.

    \section1 License Information

    The QtHelp module uses the CLucene indexing library to provide full-text
    searching capabilities for Qt Assistant and applications that use the
    features of QtHelp.

    Qt Commercial Edition licensees that wish to distribute applications that
    use these features of the QtHelp module need to be aware of their
    obligations under the GNU Lesser General Public License (LGPL). 

    Developers using the Open Source Edition can choose to redistribute
    the module under the appropriate version of the GNU LGPL; version 2.1
    for applications and libraries licensed under the GNU GPL version 2,
    or version 3 for applications and libraries licensed under the GNU
    GPL version 3.

    \legalese
    Copyright (C) 2003-2006 Ben van Klinken and the CLucene Team \BR
    Changes are Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
    \endlegalese
*/

/*!
    \page qthelpproject.html
    \title Qt Help Project
    
    A Qt help project collects all data necessary to generate a
    compressed help file. Along with the actual help data, like
    the table of contents, index keywords and help documents, it
    contains some extra information like a namespace to identify
    the help file. One help project stands for one documentation,
    e.g. the Qt Assistant manual.
    
    \section1 Qt Help Project File Format
    
    The file format is XML based. For a better understanding of
    the format we'll discuss the following example:
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 7
    
    \section2 Namespace
    
    To enable the QHelpEngine to retrieve the proper documentation to
    a given link, every documentation set has to have a unique
    identifier. A unique identifier makes is also possible for the
    help collection to keep track of a documentation set without relying
    on its file name. The Qt help system uses a namespace as identifier
    which is defined by the mandatory namespace tags. In the example
    above, the namespace is "mycompany.com.myapplication.1_0".
    
    \target Virtual Folders
    \section2 Virtual Folders
    
    Having a namespace for every documentation naturally means that
    the documentation sets are quite separated. From the help engines
    point of view this is beneficial, but from the documentors view
    it is often desirable to cross reference certain topic from one
    manual to another without having to specify absolute links. To
    solve this problem, the help system introduced the concept of
    virtual folders.
          
    A virtual folder will become the root directory of all files
    referenced in a compressed help file. When two documentations
    share the same virtual folder, they can use relative paths when
    defining hyperlinks pointing to the other documentation. If a
    file is contained in both documentations or manuals, the one
    from the current manual has precedence over the other.
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 8
    
    The above example specifies 'doc' as virtual folder. If another
    manual, e.g. for a small helper tool for 'My Application'
    specifies the same folder, it is sufficient to write
    'doc.html#section1' to reference the first section in the
    'My Application' manual.
    
    The virtual folder tag is mandatory and the folder must not
    contain any '/'.
   
    \target Custom Filters
    \section2 Custom Filters
        
    Next in the Qt help project file are the optional definitions of
    custom filters. A custom filter contains a list of filter 
    attributes which will be used later to display only the documentation
    which has all those attributes assigned to. So, when setting the
    current filter in the QHelpEngine to "My Application 1.0" only
    the documentation which has "myapp" and "1.0" set as filter
    attributes will be shown.
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 9
    
    It is possible to define any number of custom filters in a help
    project file. Important to know is, that the filter attributes have
    not to be specified in the same project file; they can be defined
    in any other help file. The definition of a filter attributes
    takes place by specifying them in a filter section.
    
    \target Filter Section
    \section2 Filter Section    
    
    A filter section contains the actual documentation. One Qt help project
    file may contain more than one filter sections. Every filter section
    consists of four parts, the filter attributes section, the table of
    contents, the keywords and the files list. In theory all parts are
    optional but not specifying anything there will result in an empty
    documentation.
    
    \section3 Filter Attributes
    
    Every filter section should have filter attributes assigned to it, to
    enable documentation filtering. If no filter attribute is defined, the
    documentation will only be shown if no filtering occurs, meaning the
    current custom filter in the QHelpEngine does not contain any filter
    attributes.
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 10
    
    In this case, the filter attributes 'myapp' and '1.0' are assigned
    to the filter section, i.e. all contents specified in this section
    will only be shown if the current custom filter has 'myapp' or '1.0'
    or both as filter attributes.
    
    \section3 Table of contents
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 11
    
    One section tag represents one item in the table of contents. The
    sections can be nested to any degree, but from a users perspective
    it shouldn't be more than four or five levels. A section is defined
    by its title and reference. The reference, like all file references
    in a Qt help project file are relative to the help project file
    itself.
    
    \section3 Keywords
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 12
    
    The keyword section lists all keywords of this filter section. A
    keyword consists basically of a name and a file reference. If the
    attribute 'name' is used then the keyword specified there will appear in
    the visible index, i.e. it will be accessible through the QHelpIndexModel.
    If 'id' is used, the keyword does not appear in the index and is
    only accessible via the linksForIdentifier() function of the
    QHelpEngineCore. 'name' and 'id' can be specified at the same time.
    
    \section3 Files
    
    \snippet doc/src/snippets/code/doc_src_qthelp.qdoc 13
    
    Finally, the actual documentation files have to be listed. Make sure
    that all files neccessary to display the help are mentioned, i.e. 
    stylesheets or similar files need to be there as well. All listed files
    will be compressed and written to the Qt compressed help file. So, in the
    end, one single Qt help file contains all documentation files along with
    the contents and indices.
*/