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Breadcrumbs go here --> <li><a href="all-examples.html">Examples</a></li> <li>QML Examples & Demos</li> <li>Chapter 5: Using List Property Types</li> </ul> </div> <div class="toolbuttons toolblock"> <ul> <li id="smallA" class="t_button">A</li> <li id="medA" class="t_button active">A</li> <li id="bigA" class="t_button">A</li> <li id="print" class="t_button"><a href="javascript:this.print();"> <span>Print</span></a></li> </ul> </div> </div> <div class="content mainContent"> <h1 class="title">Chapter 5: Using List Property Types</h1> <span class="subtitle"></span> <!-- $$$declarative/tutorials/extending/chapter5-listproperties-description --> <div class="descr"> <a name="details"></a> <p>Files:</p> <ul> <li><a href="declarative-tutorials-extending-chapter5-listproperties-app-qml.html">declarative/tutorials/extending/chapter5-listproperties/app.qml</a></li> <li><a href="declarative-tutorials-extending-chapter5-listproperties-piechart-cpp.html">declarative/tutorials/extending/chapter5-listproperties/piechart.cpp</a></li> <li><a href="declarative-tutorials-extending-chapter5-listproperties-piechart-h.html">declarative/tutorials/extending/chapter5-listproperties/piechart.h</a></li> <li><a href="declarative-tutorials-extending-chapter5-listproperties-pieslice-cpp.html">declarative/tutorials/extending/chapter5-listproperties/pieslice.cpp</a></li> <li><a href="declarative-tutorials-extending-chapter5-listproperties-pieslice-h.html">declarative/tutorials/extending/chapter5-listproperties/pieslice.h</a></li> <li><a href="declarative-tutorials-extending-chapter5-listproperties-main-cpp.html">declarative/tutorials/extending/chapter5-listproperties/main.cpp</a></li> <li><a href="declarative-tutorials-extending-chapter5-listproperties-chapter5-listproperties-pro.html">declarative/tutorials/extending/chapter5-listproperties/chapter5-listproperties.pro</a></li> </ul> <p>Right now, a <tt>PieChart</tt> can only have one <tt>PieSlice</tt>. Ideally a chart would have multiple slices, with different colors and sizes. To do this, we could have a <tt>slices</tt> property that accepts a list of <tt>PieSlice</tt> items:</p> <pre class="qml"> import Charts 1.0 import QtQuick 1.0 <span class="type"><a href="qml-item.html">Item</a></span> { <span class="name">width</span>: <span class="number">300</span>; <span class="name">height</span>: <span class="number">200</span> <span class="type">PieChart</span> { <span class="name">anchors</span>.centerIn: <span class="name">parent</span> <span class="name">width</span>: <span class="number">100</span>; <span class="name">height</span>: <span class="number">100</span> <span class="name">slices</span>: [ <span class="type">PieSlice</span> { <span class="name">anchors</span>.fill: <span class="name">parent</span> <span class="name">color</span>: <span class="string">"red"</span> <span class="name">fromAngle</span>: <span class="number">0</span>; <span class="name">angleSpan</span>: <span class="number">110</span> }, <span class="type">PieSlice</span> { <span class="name">anchors</span>.fill: <span class="name">parent</span> <span class="name">color</span>: <span class="string">"black"</span> <span class="name">fromAngle</span>: <span class="number">110</span>; <span class="name">angleSpan</span>: <span class="number">50</span> }, <span class="type">PieSlice</span> { <span class="name">anchors</span>.fill: <span class="name">parent</span> <span class="name">color</span>: <span class="string">"blue"</span> <span class="name">fromAngle</span>: <span class="number">160</span>; <span class="name">angleSpan</span>: <span class="number">100</span> } ] } }</pre> <p class="centerAlign"><img src="images/extending-tutorial-chapter5.png" alt="" /></p><p>To do this, we replace the <tt>pieSlice</tt> property in <tt>PieChart</tt> with a <tt>slices</tt> property, declared as a <a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a> type. The <a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a> class enables the creation of list properties in QML extensions. We replace the <tt>pieSlice()</tt> function with a <tt>slices()</tt> function that returns a list of slices, and add an internal <tt>append_slice()</tt> function (discussed below). We also use a <a href="qlist.html">QList</a> to store the internal list of slices as <tt>m_slices</tt>:</p> <pre class="cpp"> <span class="keyword">class</span> PieChart : <span class="keyword">public</span> <span class="type"><a href="qdeclarativeitem.html">QDeclarativeItem</a></span> { Q_OBJECT Q_PROPERTY(<span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>PieSlice<span class="operator">></span> slices READ slices) ... <span class="keyword">public</span>: ... <span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>PieSlice<span class="operator">></span> slices(); <span class="keyword">private</span>: <span class="keyword">static</span> <span class="type">void</span> append_slice(<span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>PieSlice<span class="operator">></span> <span class="operator">*</span>list<span class="operator">,</span> PieSlice <span class="operator">*</span>slice); <span class="type"><a href="qstring.html">QString</a></span> m_name; <span class="type"><a href="qlist.html">QList</a></span><span class="operator"><</span>PieSlice <span class="operator">*</span><span class="operator">></span> m_slices; };</pre> <p>Although the <tt>slices</tt> property does not have an associated <tt>WRITE</tt> function, it is still modifiable because of the way <a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a> works. In the <tt>PieChart</tt> implementation, we implement <tt>PieChart::slices()</tt> to return a <a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a> value and indicate that the internal <tt>PieChart::append_slice()</tt> function is to be called whenever a request is made from QML to add items to the list:</p> <pre class="cpp"> <span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>PieSlice<span class="operator">></span> PieChart<span class="operator">::</span>slices() { <span class="keyword">return</span> <span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>PieSlice<span class="operator">></span>(<span class="keyword">this</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="operator">&</span>PieChart<span class="operator">::</span>append_slice); } <span class="type">void</span> PieChart<span class="operator">::</span>append_slice(<span class="type"><a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a></span><span class="operator"><</span>PieSlice<span class="operator">></span> <span class="operator">*</span>list<span class="operator">,</span> PieSlice <span class="operator">*</span>slice) { PieChart <span class="operator">*</span>chart <span class="operator">=</span> qobject_cast<span class="operator"><</span>PieChart <span class="operator">*</span><span class="operator">></span>(list<span class="operator">-</span><span class="operator">></span>object); <span class="keyword">if</span> (chart) { slice<span class="operator">-</span><span class="operator">></span>setParentItem(chart); chart<span class="operator">-</span><span class="operator">></span>m_slices<span class="operator">.</span>append(slice); } }</pre> <p>The <tt>append_slice()</tt> function simply sets the parent item as before, and adds the new item to the <tt>m_slices</tt> list. As you can see, the append function for a <a href="qdeclarativelistproperty.html">QDeclarativeListProperty</a> is called with two arguments: the list property, and the item that is to be appended.</p> <p>The <tt>PieSlice</tt> class has also been modified to include <tt>fromAngle</tt> and <tt>angleSpan</tt> properties and to draw the slice according to these values. This is a straightforward modification if you have read the previous pages in this tutorial, so the code is not shown here.</p> <p>The complete code can be seen in the updated <tt>examples/tutorials/extending/chapter5-listproperties</tt> directory.</p> </div> <!-- @@@declarative/tutorials/extending/chapter5-listproperties --> </div> </div> </div> <div class="ft"> <span></span> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2015 The Qt Company Ltd. 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