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54 \page qtscriptextensions.html
55 \title Creating QtScript Extensions
57 \brief A guide to creating and using QtScript extensions.
59 QtScript extensions can make additional functionality available to scripts
60 evaluated by a QScriptEngine. Extensions are imported by calling
61 the QScriptEngine::importExtension() function.
63 There are three ways to create an extension:
66 \o Subclass QScriptExtensionPlugin and implement the desired functionality.
67 \o Implement the functionality in a script file.
68 \o Use a hybrid approach, where part of the functionality is implemented in a
69 QScriptExtensionPlugin, and part is implemented in a script file.
72 The (dot-qualified) extension name is used to determine the path (relative to
73 the application's plugin path) where QScriptEngine will look for the script
74 file that will initialize the extension; if a file called \c{__init__.js}
75 (usually located in \c{[application plugin path]/script/foo/}) is
76 found in the corresponding folder, its contents will be evaluated by the engine
77 when the extension is imported.
78 As an example, if the extension is called \c{"foo.bar.baz"}, the engine will look
79 for \c{__init__.js} in \c{foo/bar/baz}. Additionally, before importing
80 \c{"foo.bar.baz"}, the engine will ensure that the extensions \c{"foo"} and \c{"foo.bar"}
81 are imported, locating and evaluating the corresponding \c{__init__.js}
82 in the same manner (in folders \c{foo} and \c{foo/bar}, respectively).
84 The contents of \c{__init__.js} are evaluated in a new QScriptContext,
85 as if it were the body of a function. The engine's Global Object acts as
86 the \c{this} object. The following local variables are initially available
90 \o \bold{__extension__}: The name of the extension (e.g. \c{"foo.bar.baz"}).
91 \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().)
92 \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.
95 An example of a simple \c{__init__.js}:
97 \snippet doc/src/snippets/code/doc_src_qtscriptextensions.qdoc 0
99 QScriptEngine will look for a QScriptExtensionPlugin that provides
100 the relevant extension by querying each plugin for its keys()
101 until a match is found. The plugin's initialize() function will be
102 called \bold{after} the relevant \c{__init__.js} (if any) has been
105 Continuining with the example of our imaginary extension \c{"foo.bar.baz"},
106 the following steps will be performed by QScriptEngine::importExtension():
109 \o If it exists, \c{foo/__init__.js} is evaluated.
110 \o If a plugin with \c{"foo"} in its list of keys is found, its initialize() function is called with \c{"foo"} as key.
111 \o If it exists, \c{foo/bar/__init__.js} is evaluated.
112 \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.
113 \o If it exists, \c{foo/bar/baz/__init__.js} is evaluated.
114 \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.
117 \section1 Static Extensions
119 When an extension is compiled and linked into your application as a
120 static plugin, Qt Script will look for the optional \c{__init__.js}
121 script in a resource, prefixed by \c{:/qtscriptextension}. For example,
122 if the extension key is "foo.bar", Qt Script will evaluate the contents
123 of the file \c{:/qtscriptextension/foo/bar/__init__.js}, if it
124 exists. Note that if the resource is built into the plugin, you may
125 need to use the Q_INIT_RESOURCE() macro to initialize the resource
126 before importing the extension.