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/*!

    \group helpsystem

    \title Help System

    \ingroup groups

    \brief Classes used to provide online-help for applications.

    \keyword help system

    These classes provide for all forms of online-help in your application,

    with three levels of detail:

    \list 1

        \o Tool Tips and Status Bar message - flyweight help, extremely brief,

            entirely integrated in the user interface, requiring little

            or no user interaction to invoke.

        \o What's This? - lightweight, but can be

            a three-paragraph explanation.

        \o Online Help - can encompass any amount of information,

            but is typically slower to call up, somewhat separated

            from the user's work, and often users feel that using online

            help is a digression from their real task.

    \endlist

*/

/*!

    \page qthelp-framework.html

    \title The Qt Help Framework

    \brief Integrating Documentation in Applications

    \ingroup frameworks-technologies

    \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.

*/

/*!

    \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 should not 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, are relative to the help project file itself.

    \note The referenced files must be inside the same directory (or within a

    subdirectory) as the help project file. An absolute file path is not supported

    either.

    \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. The files, like all

    file references in a Qt help project, are relative to the help project file

    itself. As the example shows, files (but not directories) can also be 

    specified as patterns using wildcards. 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. \note The referenced files must be inside the same directory 

    (or within a subdirectory) as the help project file. An absolute file path 

    is not supported either.

*/