source: trunk/doc/src/scripting/qtscriptextensions.qdoc@ 788

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/*!
    \page qtscriptextensions.html
    \title Creating QtScript Extensions
    \brief A guide to creating and using QtScript extensions.

    QtScript extensions can make additional functionality available to scripts
    evaluated by a QScriptEngine. Extensions are imported by calling
    the QScriptEngine::importExtension() function.

    There are three ways to create an extension:

    \list
    \o Subclass QScriptExtensionPlugin and implement the desired functionality.
    \o Implement the functionality in a script file.
    \o Use a hybrid approach, where part of the functionality is implemented in a
       QScriptExtensionPlugin, and part is implemented in a script file.
    \endlist

    The (dot-qualified) extension name is used to determine the path (relative to
    the application's plugin path) where QScriptEngine will look for the script
    file that will initialize the extension; if a file called \c{__init__.js}
    (usually located in \c{[application plugin path]/script/foo/}) is
    found in the corresponding folder, its contents will be evaluated by the engine
    when the extension is imported.
    As an example, if the extension is called \c{"foo.bar.baz"}, the engine will look
    for \c{__init__.js} in \c{foo/bar/baz}. Additionally, before importing
    \c{"foo.bar.baz"}, the engine will ensure that the extensions \c{"foo"} and \c{"foo.bar"}
    are imported, locating and evaluating the corresponding \c{__init__.js}
    in the same manner (in folders \c{foo} and \c{foo/bar}, respectively).

    The contents of \c{__init__.js} are evaluated in a new QScriptContext,
    as if it were the body of a function. The engine's Global Object acts as
    the \c{this} object. The following local variables are initially available
    to the script:

    \list
    \o \bold{__extension__}: The name of the extension (e.g. \c{"foo.bar.baz"}).
    \o \bold{__setupPackage__}: A convenience function for setting up a "namespace" in the script environment. A typical application is to call \c{__setupPackage__()} with \c{__extension__} as argument; e.g. \c{__setupPackage__("foo.bar.baz")} would ensure that the object chain represented by the expression \c{foo.bar.baz} exists in the script environment. (This function is semantically equivalent to QScriptExtensionPlugin::setupPackage().)
    \o \bold{__postInit__}: By default, this variable is undefined. If you assign a function to it, that function will be called \bold{after} the C++ plugin's initialize() function has been called. You can use this to perform further initialization that depends on e.g. native functions that the C++ plugin registers.
    \endlist

    An example of a simple \c{__init__.js}:

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

    QScriptEngine will look for a QScriptExtensionPlugin that provides
    the relevant extension by querying each plugin for its keys()
    until a match is found. The plugin's initialize() function will be
    called \bold{after} the relevant \c{__init__.js} (if any) has been
    evaluated.

    Continuining with the example of our imaginary extension \c{"foo.bar.baz"},
    the following steps will be performed by QScriptEngine::importExtension():

    \list
    \o If it exists, \c{foo/__init__.js} is evaluated.
    \o If a plugin with \c{"foo"} in its list of keys is found, its initialize() function is called with \c{"foo"} as key.
    \o If it exists, \c{foo/bar/__init__.js} is evaluated.
    \o If a plugin with \c{"foo.bar"} in its list of keys is found, its initialize() function is called with \c{"foo.bar"} as key.
    \o If it exists, \c{foo/bar/baz/__init__.js} is evaluated.
    \o If a plugin with "foo.bar.baz" in its list of keys is found, its initialize() function is called with \c{"foo.bar.baz"} as key.
    \endlist

    \section1 Static Extensions

    When an extension is compiled and linked into your application as a
    static plugin, Qt Script will look for the optional \c{__init__.js}
    script in a resource, prefixed by \c{:/qtscriptextension}. For example,
    if the extension key is "foo.bar", Qt Script will evaluate the contents
    of the file \c{:/qtscriptextension/foo/bar/__init__.js}, if it
    exists. Note that if the resource is built into the plugin, you may
    need to use the Q_INIT_RESOURCE() macro to initialize the resource
    before importing the extension.
*/