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<li>Qt 5.2</li>
<li><a href="qtscript-index.html">Qt Script</a></li>
<li>Creating Qt Script Extensions</li>
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Qt 5.2.1 Reference Documentation</li>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#static-extensions">Static Extensions</a></li>
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<h1 class="title">Creating Qt Script Extensions</h1>
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<p>Qt Script extensions can make additional functionality available to scripts evaluated by a <a href="qscriptengine.html">QScriptEngine</a>. Extensions are imported by calling the <a href="qscriptengine.html#importExtension">QScriptEngine::importExtension</a>() function.</p>
<p>There are three ways to create an extension:</p>
<ul>
<li>Subclass <a href="qscriptextensionplugin.html">QScriptExtensionPlugin</a> and implement the desired functionality.</li>
<li>Implement the functionality in a script file.</li>
<li>Use a hybrid approach, where part of the functionality is implemented in a <a href="qscriptextensionplugin.html">QScriptExtensionPlugin</a>, and part is implemented in a script file.</li>
</ul>
<p>The (dot-qualified) extension name is used to determine the path (relative to the application's plugin path) where <a href="qscriptengine.html">QScriptEngine</a> will look for the script file that will initialize the extension; if a file called <tt>__init__.js</tt> (usually located in <tt>[application plugin path]/script/foo/</tt>) 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 <tt>"foo.bar.baz"</tt>, the engine will look for <tt>__init__.js</tt> in <tt>foo/bar/baz</tt>. Additionally, before importing <tt>"foo.bar.baz"</tt>, the engine will ensure that the extensions <tt>"foo"</tt> and <tt>"foo.bar"</tt> are imported, locating and evaluating the corresponding <tt>__init__.js</tt> in the same manner (in folders <tt>foo</tt> and <tt>foo/bar</tt>, respectively).</p>
<p>The contents of <tt>__init__.js</tt> are evaluated in a new <a href="qscriptcontext.html">QScriptContext</a>, as if it were the body of a function. The engine's Global Object acts as the <tt>this</tt> object. The following local variables are initially available to the script:</p>
<ul>
<li><b>__extension__</b>: The name of the extension (e.g. <tt>"foo.bar.baz"</tt>).</li>
<li><b>__setupPackage__</b>: A convenience function for setting up a "namespace" in the script environment. A typical application is to call <tt>__setupPackage__()</tt> with <tt>__extension__</tt> as argument; e.g. <tt>__setupPackage__("foo.bar.baz")</tt> would ensure that the object chain represented by the expression <tt>foo.bar.baz</tt> exists in the script environment. (This function is semantically equivalent to <a href="qscriptextensionplugin.html#setupPackage">QScriptExtensionPlugin::setupPackage</a>().)</li>
<li><b>__postInit__</b>: By default, this variable is undefined. If you assign a function to it, that function will be called <b>after</b> 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.</li>
</ul>
<p>An example of a simple <tt>__init__.js</tt>:</p>
<pre class="js"><span class="name">print</span>(<span class="string">"importing "</span> <span class="operator">+</span> <span class="name">__extension__</span>);
<span class="name">__setupPackage__</span>(<span class="string">"cool.stuff"</span>);
<span class="name">cool</span>.<span class="name">stuff</span>.<span class="name">add</span> <span class="operator">=</span> <span class="keyword">function</span>(<span class="name">a</span>, b) { <span class="keyword">return</span> <span class="name">a</span> <span class="operator">+</span> <span class="name">b</span>; }
<span class="name">cool</span>.<span class="name">stuff</span>.<span class="name">subtract</span> <span class="operator">=</span> <span class="keyword">function</span>(<span class="name">a</span>, b) { <span class="keyword">return</span> <span class="name">a</span> <span class="operator">-</span> <span class="name">b</span>; }</pre>
<p><a href="qscriptengine.html">QScriptEngine</a> will look for a <a href="qscriptextensionplugin.html">QScriptExtensionPlugin</a> 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 <b>after</b> the relevant <tt>__init__.js</tt> (if any) has been evaluated.</p>
<p>Continuining with the example of our imaginary extension <tt>"foo.bar.baz"</tt>, the following steps will be performed by <a href="qscriptengine.html#importExtension">QScriptEngine::importExtension</a>():</p>
<ul>
<li>If it exists, <tt>foo/__init__.js</tt> is evaluated.</li>
<li>If a plugin with <tt>"foo"</tt> in its list of keys is found, its initialize() function is called with <tt>"foo"</tt> as key.</li>
<li>If it exists, <tt>foo/bar/__init__.js</tt> is evaluated.</li>
<li>If a plugin with <tt>"foo.bar"</tt> in its list of keys is found, its initialize() function is called with <tt>"foo.bar"</tt> as key.</li>
<li>If it exists, <tt>foo/bar/baz/__init__.js</tt> is evaluated.</li>
<li>If a plugin with "foo.bar.baz" in its list of keys is found, its initialize() function is called with <tt>"foo.bar.baz"</tt> as key.</li>
</ul>
<a name="static-extensions"></a>
<h2>Static Extensions</h2>
<p>When an extension is compiled and linked into your application as a static plugin, Qt Script will look for the optional <tt>__init__.js</tt> script in a resource, prefixed by <tt>:/qtscriptextension</tt>. For example, if the extension key is "foo.bar", Qt Script will evaluate the contents of the file <tt>:/qtscriptextension/foo/bar/__init__.js</tt>, 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.</p>
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