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<td >Qt 5.12</td><td ><a href="qtcore-index.html">Qt Core</a></td><td ><a href="qtcore-module.html">C++ Classes</a></td><td >QEnableSharedFromThis</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtcore-index.html">Qt 5.12.6 Reference Documentation</a></td>
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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">QEnableSharedFromThis Class</h1>
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<p>A base class that allows obtaining a <a href="qsharedpointer.html">QSharedPointer</a> for an object already managed by a shared pointer. <a href="#details">More...</a></p>
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<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QEnableSharedFromThis></span>
</td></tr><tr><td class="memItemLeft rightAlign topAlign"> qmake:</td><td class="memItemRight bottomAlign"> QT += core</td></tr><tr><td class="memItemLeft rightAlign topAlign"> Since:</td><td class="memItemRight bottomAlign"> Qt 5.4</td></tr></table></div><ul>
<li><a href="qenablesharedfromthis-members.html">List of all members, including inherited members</a></li>
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<a name="public-functions"></a>
<h2 id="public-functions">Public Functions</h2>
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<tr><td class="memItemLeft rightAlign topAlign"> QSharedPointer<T> </td><td class="memItemRight bottomAlign"><b><a href="qenablesharedfromthis.html#sharedFromThis">sharedFromThis</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QSharedPointer<const T> </td><td class="memItemRight bottomAlign"><b><a href="qenablesharedfromthis.html#sharedFromThis-1">sharedFromThis</a></b>() const</td></tr>
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<div class="descr">
<h2 id="details">Detailed Description</h2>
<p>A base class that allows obtaining a <a href="qsharedpointer.html">QSharedPointer</a> for an object already managed by a shared pointer.</p>
<p>You can inherit this class when you need to create a <a href="qsharedpointer.html">QSharedPointer</a> from any instance of a class; for instance, from within the object itself. The key point is that the technique of just returning <a href="qsharedpointer.html">QSharedPointer</a><T>(this) can not be used, because this winds up creating multiple distinct <a href="qsharedpointer.html">QSharedPointer</a> objects with separate reference counts. For this reason you must never create more than one <a href="qsharedpointer.html">QSharedPointer</a> from the same raw pointer.</p>
<p><a href="qenablesharedfromthis.html">QEnableSharedFromThis</a> defines two member functions called <a href="qenablesharedfromthis.html#sharedFromThis">sharedFromThis</a>() that return a <a href="qsharedpointer.html">QSharedPointer</a><T> and <a href="qsharedpointer.html">QSharedPointer</a><const T>, depending on constness, to <code>this</code>:</p>
<pre class="cpp">
<span class="keyword">class</span> Y: <span class="keyword">public</span> <span class="type"><a href="qenablesharedfromthis.html">QEnableSharedFromThis</a></span><span class="operator"><</span>Y<span class="operator">></span>
{
<span class="keyword">public</span>:
<span class="type"><a href="qsharedpointer.html">QSharedPointer</a></span><span class="operator"><</span>Y<span class="operator">></span> f()
{
<span class="keyword">return</span> sharedFromThis();
}
};
<span class="type">int</span> main()
{
<span class="type"><a href="qsharedpointer.html">QSharedPointer</a></span><span class="operator"><</span>Y<span class="operator">></span> p(<span class="keyword">new</span> Y());
<span class="type"><a href="qsharedpointer.html">QSharedPointer</a></span><span class="operator"><</span>Y<span class="operator">></span> y <span class="operator">=</span> p<span class="operator">-</span><span class="operator">></span>f();
Q_ASSERT(p <span class="operator">=</span><span class="operator">=</span> y); <span class="comment">// p and q must share ownership</span>
}
</pre>
<p>It is also possible to get a shared pointer from an object outside of the class itself. This is especially useful in code that provides an interface to scripts, where it is currently not possible to use shared pointers. For example:</p>
<pre class="cpp">
<span class="keyword">class</span> ScriptInterface : <span class="keyword">public</span> <span class="type"><a href="qobject.html">QObject</a></span>
{
Q_OBJECT
<span class="comment">// ...</span>
<span class="keyword">public</span> <span class="keyword">slots</span>:
<span class="type">void</span> slotCalledByScript(Y <span class="operator">*</span>managedBySharedPointer)
{
<span class="type"><a href="qsharedpointer.html">QSharedPointer</a></span><span class="operator"><</span>Y<span class="operator">></span> yPtr <span class="operator">=</span> managedBySharedPointer<span class="operator">-</span><span class="operator">></span>sharedFromThis();
<span class="comment">// Some other code unrelated to scripts that expects a QSharedPointer<Y> ...</span>
}
};
</pre>
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<h2>Member Function Documentation</h2>
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<h3 class="fn" id="sharedFromThis"><a name="sharedFromThis"></a><span class="type"><a href="qsharedpointer.html">QSharedPointer</a></span><<span class="type">T</span>> QEnableSharedFromThis::<span class="name">sharedFromThis</span>()</h3>
<p>If <code>this</code> (that is, the subclass instance invoking this method) is being managed by a <a href="qsharedpointer.html">QSharedPointer</a>, returns a shared pointer instance pointing to <code>this</code>; otherwise returns a <a href="qsharedpointer.html">QSharedPointer</a> holding a null pointer.</p>
<p>This function was introduced in Qt 5.4.</p>
<!-- @@@sharedFromThis -->
<!-- $$$sharedFromThis$$$sharedFromThis -->
<h3 class="fn" id="sharedFromThis-1"><a name="sharedFromThis-1"></a><span class="type"><a href="qsharedpointer.html">QSharedPointer</a></span><const <span class="type">T</span>> QEnableSharedFromThis::<span class="name">sharedFromThis</span>() const</h3>
<p>This is an overloaded function.</p>
<p>Const overload of <a href="qenablesharedfromthis.html#sharedFromThis">sharedFromThis</a>().</p>
<p>This function was introduced in Qt 5.4.</p>
<!-- @@@sharedFromThis -->
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