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<?xml version="1.0" encoding="UTF-8"?>
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<title>Qt 4.8: Extending QML - Default Property Example</title>
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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<li>Extending QML - Default Property Example</li>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#declaring-the-birthdayparty-class">Declaring the BirthdayParty class</a></li>
<li class="level1"><a href="#running-the-example">Running the example</a></li>
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<h1 class="title">Extending QML - Default Property Example</h1>
<span class="subtitle"></span>
<!-- $$$declarative/cppextensions/referenceexamples/default-description -->
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<p>Files:</p>
<ul>
<li><a href="declarative-cppextensions-referenceexamples-default-birthdayparty-cpp.html">declarative/cppextensions/referenceexamples/default/birthdayparty.cpp</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-birthdayparty-h.html">declarative/cppextensions/referenceexamples/default/birthdayparty.h</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-example-qml.html">declarative/cppextensions/referenceexamples/default/example.qml</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-person-cpp.html">declarative/cppextensions/referenceexamples/default/person.cpp</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-person-h.html">declarative/cppextensions/referenceexamples/default/person.h</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-main-cpp.html">declarative/cppextensions/referenceexamples/default/main.cpp</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-default-pro.html">declarative/cppextensions/referenceexamples/default/default.pro</a></li>
<li><a href="declarative-cppextensions-referenceexamples-default-default-qrc.html">declarative/cppextensions/referenceexamples/default/default.qrc</a></li>
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<p>This example builds on:</p>
<ul>
<li><a href="declarative-cppextensions-referenceexamples-coercion.html">Extending QML - Inheritance and Coercion Example</a></li>
<li><a href="declarative-cppextensions-referenceexamples-properties.html">Extending QML - Object and List Property Types Example</a></li>
<li><a href="declarative-cppextensions-referenceexamples-adding.html">Extending QML - Adding Types Example</a></li>
</ul>
<p>The Default Property Example is a minor modification of the <a href="declarative-cppextensions-referenceexamples-coercion.html">Extending QML - Inheritance and Coercion Example</a> that simplifies the specification of a BirthdayParty through the use of a default property.</p>
<pre class="qml"> <span class="type">BirthdayParty</span> {
<span class="name">host</span>: <span class="name">Boy</span> {
<span class="name">name</span>: <span class="string">"Bob Jones"</span>
<span class="name">shoeSize</span>: <span class="number">12</span>
}
<span class="type">Boy</span> { <span class="name">name</span>: <span class="string">"Leo Hodges"</span> }
<span class="type">Boy</span> { <span class="name">name</span>: <span class="string">"Jack Smith"</span> }
<span class="type">Girl</span> { <span class="name">name</span>: <span class="string">"Anne Brown"</span> }
}</pre>
<a name="declaring-the-birthdayparty-class"></a>
<h2>Declaring the BirthdayParty class</h2>
<p>The only difference between this example and the last, is the addition of the <tt>DefaultProperty</tt> class info annotation.</p>
<pre class="cpp"> <span class="keyword">class</span> BirthdayParty : <span class="keyword">public</span> <span class="type"><a href="qobject.html">QObject</a></span>
{
Q_OBJECT
Q_PROPERTY(Person <span class="operator">*</span>host READ host WRITE setHost)
Q_PROPERTY(<span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>Person<span class="operator">></span> guests READ guests)
Q_CLASSINFO(<span class="string">"DefaultProperty"</span><span class="operator">,</span> <span class="string">"guests"</span>)
<span class="keyword">public</span>:
BirthdayParty(<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>);
Person <span class="operator">*</span>host() <span class="keyword">const</span>;
<span class="type">void</span> setHost(Person <span class="operator">*</span>);
<span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>Person<span class="operator">></span> guests();
<span class="type">int</span> guestCount() <span class="keyword">const</span>;
Person <span class="operator">*</span>guest(<span class="type">int</span>) <span class="keyword">const</span>;
<span class="keyword">private</span>:
Person <span class="operator">*</span>m_host;
<span class="type"><a href="qlist.html">QList</a></span><span class="operator"><</span>Person <span class="operator">*</span><span class="operator">></span> m_guests;
};</pre>
<p>The default property specifies the property to assign to whenever an explicit property is not specified, in the case of the BirthdayParty element the guest property. It is purely a syntactic simplification, the behavior is identical to specifying the property by name, but it can add a more natural feel in many situations. The default property must be either an object or list property.</p>
<a name="running-the-example"></a>
<h2>Running the example</h2>
<p>The main.cpp file in the example includes a simple shell application that loads and runs the QML snippet shown at the beginning of this page.</p>
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