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<title>Qt 4.8: QAbstractFileEngineHandler Class Reference</title>
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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#public-functions">Public Functions</a></li>
<li class="level1"><a href="#details">Detailed Description</a></li>
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<h1 class="title">QAbstractFileEngineHandler Class Reference</h1>
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<p>The QAbstractFileEngineHandler class provides a way to register custom file engines with your application. <a href="#details">More...</a></p>
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<pre class="cpp"> <span class="preprocessor">#include <QAbstractFileEngineHandler></span></pre><p><b>Note:</b> All functions in this class are <a href="threads-reentrancy.html#reentrant">reentrant</a>.</p>
<p>This class was introduced in Qt 4.1.</p>
<ul>
<li><a href="qabstractfileenginehandler-members.html">List of all members, including inherited members</a></li>
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<a name="public-functions"></a>
<h2>Public Functions</h2>
<table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qabstractfileenginehandler.html#QAbstractFileEngineHandler">QAbstractFileEngineHandler</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> virtual </td><td class="memItemRight bottomAlign"><b><a href="qabstractfileenginehandler.html#dtor.QAbstractFileEngineHandler">~QAbstractFileEngineHandler</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> virtual QAbstractFileEngine * </td><td class="memItemRight bottomAlign"><b><a href="qabstractfileenginehandler.html#create">create</a></b> ( const QString & <i>fileName</i> ) const = 0</td></tr>
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<h2>Detailed Description</h2>
<p>The QAbstractFileEngineHandler class provides a way to register custom file engines with your application.</p>
<p>QAbstractFileEngineHandler is a factory for creating <a href="qabstractfileengine.html">QAbstractFileEngine</a> objects (file engines), which are used internally by <a href="qfile.html">QFile</a>, <a href="qfileinfo.html">QFileInfo</a>, and <a href="qdir.html">QDir</a> when working with files and directories.</p>
<p>When you open a file, Qt chooses a suitable file engine by passing the file name from <a href="qfile.html">QFile</a> or <a href="qdir.html">QDir</a> through an internal list of registered file engine handlers. The first handler to recognize the file name is used to create the engine. Qt provides internal file engines for working with regular files and resources, but you can also register your own <a href="qabstractfileengine.html">QAbstractFileEngine</a> subclasses.</p>
<p>To install an application-specific file engine, you subclass QAbstractFileEngineHandler and reimplement <a href="qabstractfileenginehandler.html#create">create</a>(). When you instantiate the handler (e.g. by creating an instance on the stack or on the heap), it will automatically register with Qt. (The latest registered handler takes precedence over existing handlers.)</p>
<p>For example:</p>
<pre class="cpp"> <span class="keyword">class</span> ZipEngineHandler : <span class="keyword">public</span> <span class="type">QAbstractFileEngineHandler</span>
{
<span class="keyword">public</span>:
<span class="type"><a href="qabstractfileengine.html">QAbstractFileEngine</a></span> <span class="operator">*</span>create(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>fileName) <span class="keyword">const</span>;
};
<span class="type"><a href="qabstractfileengine.html">QAbstractFileEngine</a></span> <span class="operator">*</span>ZipEngineHandler<span class="operator">::</span><a href="qabstractfileenginehandler.html#create">create</a>(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>fileName) <span class="keyword">const</span>
{
<span class="comment">// ZipEngineHandler returns a ZipEngine for all .zip files</span>
<span class="keyword">return</span> fileName<span class="operator">.</span>toLower()<span class="operator">.</span>endsWith(<span class="string">".zip"</span>) <span class="operator">?</span> <span class="keyword">new</span> ZipEngine(fileName) : <span class="number">0</span>;
}
<span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span><span class="operator">*</span>argv)
{
<span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv);
ZipEngineHandler engine;
MainWindow window;
window<span class="operator">.</span>show();
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>When the handler is destroyed, it is automatically removed from Qt.</p>
<p>The most common approach to registering a handler is to create an instance as part of the start-up phase of your application. It is also possible to limit the scope of the file engine handler to a particular area of interest (e.g. a special file dialog that needs a custom file engine). By creating the handler inside a local scope, you can precisely control the area in which your engine will be applied without disturbing file operations in other parts of your application.</p>
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<p><b>See also </b><a href="qabstractfileengine.html">QAbstractFileEngine</a> and <a href="qabstractfileengine.html#create">QAbstractFileEngine::create</a>().</p>
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<div class="func">
<h2>Member Function Documentation</h2>
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<h3 class="fn"><a name="QAbstractFileEngineHandler"></a>QAbstractFileEngineHandler::<span class="name">QAbstractFileEngineHandler</span> ()</h3>
<p>Constructs a file handler and registers it with Qt. Once created this handler's <a href="qabstractfileenginehandler.html#create">create</a>() function will be called (along with all the other handlers) for any paths used. The most recently created handler that recognizes the given path (i.e. that returns a <a href="qabstractfileengine.html">QAbstractFileEngine</a>) is used for the new path.</p>
<p><b>See also </b><a href="qabstractfileenginehandler.html#create">create</a>().</p>
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<!-- $$$~QAbstractFileEngineHandler[overload1]$$$~QAbstractFileEngineHandler -->
<h3 class="fn"><a name="dtor.QAbstractFileEngineHandler"></a>QAbstractFileEngineHandler::<span class="name">~QAbstractFileEngineHandler</span> ()<tt> [virtual]</tt></h3>
<p>Destroys the file handler. This will automatically unregister the handler from Qt.</p>
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<h3 class="fn"><a name="create"></a><span class="type"><a href="qabstractfileengine.html">QAbstractFileEngine</a></span> * QAbstractFileEngineHandler::<span class="name">create</span> ( const <span class="type"><a href="qstring.html">QString</a></span> & <i>fileName</i> ) const<tt> [pure virtual]</tt></h3>
<p>Creates a file engine for file <i>fileName</i>. Returns 0 if this file handler cannot handle <i>fileName</i>.</p>
<p>Example:</p>
<pre class="cpp"> <span class="type">QAbstractSocketEngine</span> <span class="operator">*</span>ZipEngineHandler<span class="operator">::</span>create(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>fileName) <span class="keyword">const</span>
{
<span class="comment">// ZipEngineHandler returns a ZipEngine for all .zip files</span>
<span class="keyword">return</span> fileName<span class="operator">.</span>toLower()<span class="operator">.</span>endsWith(<span class="string">".zip"</span>) <span class="operator">?</span> <span class="keyword">new</span> ZipEngine(fileName) : <span class="number">0</span>;
}</pre>
<p><b>See also </b><a href="qabstractfileengine.html#create">QAbstractFileEngine::create</a>().</p>
<!-- @@@create -->
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