<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- stardelegate.qdoc --> <title>Star Delegate Example | Qt Widgets 5.12.6</title> <link rel="stylesheet" type="text/css" href="style/offline-simple.css" /> <script type="text/javascript"> document.getElementsByTagName("link").item(0).setAttribute("href", "style/offline.css"); // loading style sheet breaks anchors that were jumped to before // so force jumping to anchor again setTimeout(function() { var anchor = location.hash; // need to jump to different anchor first (e.g. none) location.hash = "#"; setTimeout(function() { location.hash = anchor; }, 0); }, 0); </script> </head> <body> <div class="header" id="qtdocheader"> <div class="main"> <div class="main-rounded"> <div class="navigationbar"> <table><tr> <td >Qt 5.12</td><td ><a href="qtwidgets-index.html">Qt Widgets</a></td><td ><a href="examples-itemviews.html">Item Views Examples</a></td><td >Star Delegate Example</td></tr></table><table class="buildversion"><tr> <td id="buildversion" width="100%" align="right"><a href="qtwidgets-index.html">Qt 5.12.6 Reference Documentation</a></td> </tr></table> </div> </div> <div class="content"> <div class="line"> <div class="content mainContent"> <div class="sidebar"> <div class="toc"> <h3><a name="toc">Contents</a></h3> <ul> <li class="level1"><a href="#stardelegate-class-definition">StarDelegate Class Definition</a></li> <li class="level1"><a href="#stardelegate-class-implementation">StarDelegate Class Implementation</a></li> <li class="level1"><a href="#stareditor-class-definition">StarEditor Class Definition</a></li> <li class="level1"><a href="#stareditor-class-implementation">StarEditor Class Implementation</a></li> <li class="level1"><a href="#starrating-class-definition">StarRating Class Definition</a></li> <li class="level1"><a href="#starrating-class-implementation">StarRating Class Implementation</a></li> <li class="level1"><a href="#the-main-function">The <code>main()</code> Function</a></li> <li class="level1"><a href="#possible-extensions-and-suggestions">Possible Extensions and Suggestions</a></li> </ul> </div> <div class="sidebar-content" id="sidebar-content"></div></div> <h1 class="title">Star Delegate Example</h1> <span class="subtitle"></span> <!-- $$$itemviews/stardelegate-brief --> <p>The Star Delegate example shows how to create a delegate that can paint itself and that supports editing.</p> <!-- @@@itemviews/stardelegate --> <!-- $$$itemviews/stardelegate-description --> <div class="descr"> <a name="details"></a> <p class="centerAlign"><img src="images/stardelegate.png" alt="The Star Delegate Example" /></p><p>When displaying data in a <a href="qlistview.html">QListView</a>, <a href="qtableview.html">QTableView</a>, or <a href="qtreeview.html">QTreeView</a>, the individual items are drawn by a <a href="model-view-programming.html#delegate-classes">delegate</a>. Also, when the user starts editing an item (for example, by double-clicking the item), the delegate provides an editor widget that is placed on top of the item while editing takes place.</p> <p>Delegates are subclasses of <a href="qabstractitemdelegate.html">QAbstractItemDelegate</a>. Qt provides <a href="qitemdelegate.html">QItemDelegate</a>, which inherits <a href="qabstractitemdelegate.html">QAbstractItemDelegate</a> and handles the most common data types (notably <code>int</code> and <a href="../qtcore/qstring.html">QString</a>). If we need to support custom data types, or want to customize the rendering or the editing for existing data types, we can subclass <a href="qabstractitemdelegate.html">QAbstractItemDelegate</a> or <a href="qitemdelegate.html">QItemDelegate</a>. See <a href="model-view-programming.html#delegate-classes">Delegate Classes</a> for more information about delegates, and <a href="model-view-programming.html">Model/View Programming</a> if you need a high-level introduction to Qt's model/view architecture (including delegates).</p> <p>In this example, we will see how to implement a custom delegate to render and edit a "star rating" data type, which can store values such as "1 out of 5 stars".</p> <p>The example consists of the following classes:</p> <ul> <li><code>StarRating</code> is the custom data type. It stores a rating expressed as stars, such as "2 out of 5 stars" or "5 out of 6 stars".</li> <li><code>StarDelegate</code> inherits <a href="qitemdelegate.html">QItemDelegate</a> and provides support for <code>StarRating</code> (in addition to the data types already handled by <a href="qitemdelegate.html">QItemDelegate</a>).</li> <li><code>StarEditor</code> inherits <a href="qwidget.html">QWidget</a> and is used by <code>StarDelegate</code> to let the user edit a star rating using the mouse.</li> </ul> <p>To show the <code>StarDelegate</code> in action, we will fill a <a href="qtablewidget.html">QTableWidget</a> with some data and install the delegate on it.</p> <a name="stardelegate-class-definition"></a> <h2 id="stardelegate-class-definition">StarDelegate Class Definition</h2> <p>Here's the definition of the <code>StarDelegate</code> class:</p> <pre class="cpp"> <span class="keyword">class</span> StarDelegate : <span class="keyword">public</span> <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span> { Q_OBJECT <span class="keyword">public</span>: StarDelegate(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>) : <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span>(parent) {} <span class="type">void</span> paint(<span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span> <span class="operator">*</span>painter<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstyleoptionviewitem.html">QStyleOptionViewItem</a></span> <span class="operator">&</span>option<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> override; <span class="type"><a href="../qtcore/qsize.html">QSize</a></span> sizeHint(<span class="keyword">const</span> <span class="type"><a href="qstyleoptionviewitem.html">QStyleOptionViewItem</a></span> <span class="operator">&</span>option<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> override; <span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>createEditor(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstyleoptionviewitem.html">QStyleOptionViewItem</a></span> <span class="operator">&</span>option<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> override; <span class="type">void</span> setEditorData(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>editor<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> override; <span class="type">void</span> setModelData(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>editor<span class="operator">,</span> <span class="type"><a href="../qtcore/qabstractitemmodel.html">QAbstractItemModel</a></span> <span class="operator">*</span>model<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> override; <span class="keyword">private</span> <span class="keyword">slots</span>: <span class="type">void</span> commitAndCloseEditor(); }; </pre> <p>All public functions are reimplemented virtual functions from <a href="qitemdelegate.html">QItemDelegate</a> to provide custom rendering and editing.</p> <a name="stardelegate-class-implementation"></a> <h2 id="stardelegate-class-implementation">StarDelegate Class Implementation</h2> <p>The <a href="qabstractitemdelegate.html#paint">paint()</a> function is reimplemented from <a href="qitemdelegate.html">QItemDelegate</a> and is called whenever the view needs to repaint an item:</p> <pre class="cpp"> <span class="type">void</span> StarDelegate<span class="operator">::</span>paint(<span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span> <span class="operator">*</span>painter<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstyleoptionviewitem.html">QStyleOptionViewItem</a></span> <span class="operator">&</span>option<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> { <span class="keyword">if</span> (index<span class="operator">.</span>data()<span class="operator">.</span>canConvert<span class="operator"><</span>StarRating<span class="operator">></span>()) { StarRating starRating <span class="operator">=</span> qvariant_cast<span class="operator"><</span>StarRating<span class="operator">></span>(index<span class="operator">.</span>data()); <span class="keyword">if</span> (option<span class="operator">.</span>state <span class="operator">&</span> <span class="type"><a href="qstyle.html">QStyle</a></span><span class="operator">::</span>State_Selected) painter<span class="operator">-</span><span class="operator">></span>fillRect(option<span class="operator">.</span>rect<span class="operator">,</span> option<span class="operator">.</span>palette<span class="operator">.</span>highlight()); starRating<span class="operator">.</span>paint(painter<span class="operator">,</span> option<span class="operator">.</span>rect<span class="operator">,</span> option<span class="operator">.</span>palette<span class="operator">,</span> StarRating<span class="operator">::</span>ReadOnly); } <span class="keyword">else</span> { <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span><span class="operator">::</span>paint(painter<span class="operator">,</span> option<span class="operator">,</span> index); } </pre> <p>The function is invoked once for each item, represented by a <a href="../qtcore/qmodelindex.html">QModelIndex</a> object from the model. If the data stored in the item is a <code>StarRating</code>, we paint it ourselves; otherwise, we let <a href="qitemdelegate.html">QItemDelegate</a> paint it for us. This ensures that the <code>StarDelegate</code> can handle the most common data types.</p> <p>If the item is a <code>StarRating</code>, we draw the background if the item is selected, and we draw the item using <code>StarRating::paint()</code>, which we will review later.</p> <p><code>StartRating</code>s can be stored in a <a href="../qtcore/qvariant.html">QVariant</a> thanks to the <a href="../qtcore/qmetatype.html#Q_DECLARE_METATYPE">Q_DECLARE_METATYPE</a>() macro appearing in <code>starrating.h</code>. More on this later.</p> <p>The <a href="qabstractitemdelegate.html#createEditor">createEditor()</a> function is called when the user starts editing an item:</p> <pre class="cpp"> <span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>StarDelegate<span class="operator">::</span>createEditor(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstyleoptionviewitem.html">QStyleOptionViewItem</a></span> <span class="operator">&</span>option<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> { <span class="keyword">if</span> (index<span class="operator">.</span>data()<span class="operator">.</span>canConvert<span class="operator"><</span>StarRating<span class="operator">></span>()) { StarEditor <span class="operator">*</span>editor <span class="operator">=</span> <span class="keyword">new</span> StarEditor(parent); connect(editor<span class="operator">,</span> <span class="operator">&</span>StarEditor<span class="operator">::</span>editingFinished<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>StarDelegate<span class="operator">::</span>commitAndCloseEditor); <span class="keyword">return</span> editor; } <span class="keyword">else</span> { <span class="keyword">return</span> <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span><span class="operator">::</span>createEditor(parent<span class="operator">,</span> option<span class="operator">,</span> index); } } </pre> <p>If the item is a <code>StarRating</code>, we create a <code>StarEditor</code> and connect its <code>editingFinished()</code> signal to our <code>commitAndCloseEditor()</code> slot, so we can update the model when the editor closes.</p> <p>Here's the implementation of <code>commitAndCloseEditor()</code>:</p> <pre class="cpp"> <span class="type">void</span> StarDelegate<span class="operator">::</span>commitAndCloseEditor() { StarEditor <span class="operator">*</span>editor <span class="operator">=</span> qobject_cast<span class="operator"><</span>StarEditor <span class="operator">*</span><span class="operator">></span>(sender()); <span class="keyword">emit</span> commitData(editor); <span class="keyword">emit</span> closeEditor(editor); } </pre> <p>When the user is done editing, we emit <a href="qabstractitemdelegate.html#commitData">commitData()</a> and <a href="qabstractitemdelegate.html#closeEditor">closeEditor()</a> (both declared in <a href="qabstractitemdelegate.html">QAbstractItemDelegate</a>), to tell the model that there is edited data and to inform the view that the editor is no longer needed.</p> <p>The <a href="qabstractitemdelegate.html#setEditorData">setEditorData()</a> function is called when an editor is created to initialize it with data from the model:</p> <pre class="cpp"> <span class="type">void</span> StarDelegate<span class="operator">::</span>setEditorData(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>editor<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> { <span class="keyword">if</span> (index<span class="operator">.</span>data()<span class="operator">.</span>canConvert<span class="operator"><</span>StarRating<span class="operator">></span>()) { StarRating starRating <span class="operator">=</span> qvariant_cast<span class="operator"><</span>StarRating<span class="operator">></span>(index<span class="operator">.</span>data()); StarEditor <span class="operator">*</span>starEditor <span class="operator">=</span> qobject_cast<span class="operator"><</span>StarEditor <span class="operator">*</span><span class="operator">></span>(editor); starEditor<span class="operator">-</span><span class="operator">></span>setStarRating(starRating); } <span class="keyword">else</span> { <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span><span class="operator">::</span>setEditorData(editor<span class="operator">,</span> index); } } </pre> <p>We simply call <code>setStarRating()</code> on the editor.</p> <p>The <a href="qabstractitemdelegate.html#setModelData">setModelData()</a> function is called to commit data from the editor to the model when editing is finished:</p> <pre class="cpp"> <span class="type">void</span> StarDelegate<span class="operator">::</span>setModelData(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>editor<span class="operator">,</span> <span class="type"><a href="../qtcore/qabstractitemmodel.html">QAbstractItemModel</a></span> <span class="operator">*</span>model<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> { <span class="keyword">if</span> (index<span class="operator">.</span>data()<span class="operator">.</span>canConvert<span class="operator"><</span>StarRating<span class="operator">></span>()) { StarEditor <span class="operator">*</span>starEditor <span class="operator">=</span> qobject_cast<span class="operator"><</span>StarEditor <span class="operator">*</span><span class="operator">></span>(editor); model<span class="operator">-</span><span class="operator">></span>setData(index<span class="operator">,</span> <span class="type"><a href="../qtcore/qvariant.html">QVariant</a></span><span class="operator">::</span>fromValue(starEditor<span class="operator">-</span><span class="operator">></span>starRating())); } <span class="keyword">else</span> { <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span><span class="operator">::</span>setModelData(editor<span class="operator">,</span> model<span class="operator">,</span> index); } } </pre> <p>The <code>sizeHint()</code> function returns an item's preferred size:</p> <pre class="cpp"> <span class="type"><a href="../qtcore/qsize.html">QSize</a></span> StarDelegate<span class="operator">::</span>sizeHint(<span class="keyword">const</span> <span class="type"><a href="qstyleoptionviewitem.html">QStyleOptionViewItem</a></span> <span class="operator">&</span>option<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span> { <span class="keyword">if</span> (index<span class="operator">.</span>data()<span class="operator">.</span>canConvert<span class="operator"><</span>StarRating<span class="operator">></span>()) { StarRating starRating <span class="operator">=</span> qvariant_cast<span class="operator"><</span>StarRating<span class="operator">></span>(index<span class="operator">.</span>data()); <span class="keyword">return</span> starRating<span class="operator">.</span>sizeHint(); } <span class="keyword">else</span> { <span class="keyword">return</span> <span class="type"><a href="qstyleditemdelegate.html">QStyledItemDelegate</a></span><span class="operator">::</span>sizeHint(option<span class="operator">,</span> index); } } </pre> <p>We simply forward the call to <code>StarRating</code>.</p> <a name="stareditor-class-definition"></a> <h2 id="stareditor-class-definition">StarEditor Class Definition</h2> <p>The <code>StarEditor</code> class was used when implementing <code>StarDelegate</code>. Here's the class definition:</p> <pre class="cpp"> <span class="keyword">class</span> StarEditor : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span> { Q_OBJECT <span class="keyword">public</span>: StarEditor(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>); <span class="type"><a href="../qtcore/qsize.html">QSize</a></span> sizeHint() <span class="keyword">const</span> override; <span class="type">void</span> setStarRating(<span class="keyword">const</span> StarRating <span class="operator">&</span>starRating) { myStarRating <span class="operator">=</span> starRating; } StarRating starRating() { <span class="keyword">return</span> myStarRating; } <span class="keyword">signals</span>: <span class="type">void</span> editingFinished(); <span class="keyword">protected</span>: <span class="type">void</span> paintEvent(<span class="type"><a href="../qtgui/qpaintevent.html">QPaintEvent</a></span> <span class="operator">*</span>event) override; <span class="type">void</span> mouseMoveEvent(<span class="type"><a href="../qtgui/qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span>event) override; <span class="type">void</span> mouseReleaseEvent(<span class="type"><a href="../qtgui/qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span>event) override; <span class="keyword">private</span>: <span class="type">int</span> starAtPosition(<span class="type">int</span> x); StarRating myStarRating; }; </pre> <p>The class lets the user edit a <code>StarRating</code> by moving the mouse over the editor. It emits the <code>editingFinished()</code> signal when the user clicks on the editor.</p> <p>The protected functions are reimplemented from <a href="qwidget.html">QWidget</a> to handle mouse and paint events. The private function <code>starAtPosition()</code> is a helper function that returns the number of the star under the mouse pointer.</p> <a name="stareditor-class-implementation"></a> <h2 id="stareditor-class-implementation">StarEditor Class Implementation</h2> <p>Let's start with the constructor:</p> <pre class="cpp"> StarEditor<span class="operator">::</span>StarEditor(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent) : <span class="type"><a href="qwidget.html">QWidget</a></span>(parent) { setMouseTracking(<span class="keyword">true</span>); setAutoFillBackground(<span class="keyword">true</span>); } </pre> <p>We enable <a href="qwidget.html#mouseTracking-prop">mouse tracking</a> on the widget so we can follow the cursor even when the user doesn't hold down any mouse button. We also turn on <a href="qwidget.html">QWidget</a>'s <a href="qwidget.html#autoFillBackground-prop">auto-fill background</a> feature to obtain an opaque background. (Without the call, the view's background would shine through the editor.)</p> <p>The <a href="qwidget.html#paintEvent">paintEvent()</a> function is reimplemented from <a href="qwidget.html">QWidget</a>:</p> <pre class="cpp"> <span class="type">void</span> StarEditor<span class="operator">::</span>paintEvent(<span class="type"><a href="../qtgui/qpaintevent.html">QPaintEvent</a></span> <span class="operator">*</span>) { <span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span> painter(<span class="keyword">this</span>); myStarRating<span class="operator">.</span>paint(<span class="operator">&</span>painter<span class="operator">,</span> rect()<span class="operator">,</span> <span class="keyword">this</span><span class="operator">-</span><span class="operator">></span>palette()<span class="operator">,</span> StarRating<span class="operator">::</span>Editable); } </pre> <p>We simply call <code>StarRating::paint()</code> to draw the stars, just like we did when implementing <code>StarDelegate</code>.</p> <pre class="cpp"> <span class="type">void</span> StarEditor<span class="operator">::</span>mouseMoveEvent(<span class="type"><a href="../qtgui/qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span>event) { <span class="type">int</span> star <span class="operator">=</span> starAtPosition(event<span class="operator">-</span><span class="operator">></span>x()); <span class="keyword">if</span> (star <span class="operator">!</span><span class="operator">=</span> myStarRating<span class="operator">.</span>starCount() <span class="operator">&</span><span class="operator">&</span> star <span class="operator">!</span><span class="operator">=</span> <span class="operator">-</span><span class="number">1</span>) { myStarRating<span class="operator">.</span>setStarCount(star); update(); } } </pre> <p>In the mouse event handler, we call <code>setStarCount()</code> on the private data member <code>myStarRating</code> to reflect the current cursor position, and we call <a href="qwidget.html#update">QWidget::update</a>() to force a repaint.</p> <pre class="cpp"> <span class="type">void</span> StarEditor<span class="operator">::</span>mouseReleaseEvent(<span class="type"><a href="../qtgui/qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span> <span class="comment">/* event */</span>) { <span class="keyword">emit</span> editingFinished(); } </pre> <p>When the user releases a mouse button, we simply emit the <code>editingFinished()</code> signal.</p> <pre class="cpp"> <span class="type">int</span> StarEditor<span class="operator">::</span>starAtPosition(<span class="type">int</span> x) { <span class="type">int</span> star <span class="operator">=</span> (x <span class="operator">/</span> (myStarRating<span class="operator">.</span>sizeHint()<span class="operator">.</span>width() <span class="operator">/</span> myStarRating<span class="operator">.</span>maxStarCount())) <span class="operator">+</span> <span class="number">1</span>; <span class="keyword">if</span> (star <span class="operator"><</span><span class="operator">=</span> <span class="number">0</span> <span class="operator">|</span><span class="operator">|</span> star <span class="operator">></span> myStarRating<span class="operator">.</span>maxStarCount()) <span class="keyword">return</span> <span class="operator">-</span><span class="number">1</span>; <span class="keyword">return</span> star; } </pre> <p>The <code>starAtPosition()</code> function uses basic linear algebra to find out which star is under the cursor.</p> <a name="starrating-class-definition"></a> <h2 id="starrating-class-definition">StarRating Class Definition</h2> <pre class="cpp"> <span class="keyword">class</span> StarRating { <span class="keyword">public</span>: <span class="keyword">enum</span> EditMode { Editable<span class="operator">,</span> ReadOnly }; <span class="keyword">explicit</span> StarRating(<span class="type">int</span> starCount <span class="operator">=</span> <span class="number">1</span><span class="operator">,</span> <span class="type">int</span> maxStarCount <span class="operator">=</span> <span class="number">5</span>); <span class="type">void</span> paint(<span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span> <span class="operator">*</span>painter<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qrect.html">QRect</a></span> <span class="operator">&</span>rect<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtgui/qpalette.html">QPalette</a></span> <span class="operator">&</span>palette<span class="operator">,</span> EditMode mode) <span class="keyword">const</span>; <span class="type"><a href="../qtcore/qsize.html">QSize</a></span> sizeHint() <span class="keyword">const</span>; <span class="type">int</span> starCount() <span class="keyword">const</span> { <span class="keyword">return</span> myStarCount; } <span class="type">int</span> maxStarCount() <span class="keyword">const</span> { <span class="keyword">return</span> myMaxStarCount; } <span class="type">void</span> setStarCount(<span class="type">int</span> starCount) { myStarCount <span class="operator">=</span> starCount; } <span class="type">void</span> setMaxStarCount(<span class="type">int</span> maxStarCount) { myMaxStarCount <span class="operator">=</span> maxStarCount; } <span class="keyword">private</span>: <span class="type"><a href="../qtgui/qpolygonf.html">QPolygonF</a></span> starPolygon; <span class="type"><a href="../qtgui/qpolygonf.html">QPolygonF</a></span> diamondPolygon; <span class="type">int</span> myStarCount; <span class="type">int</span> myMaxStarCount; }; Q_DECLARE_METATYPE(StarRating) </pre> <p>The <code>StarRating</code> class represents a rating as a number of stars. In addition to holding the data, it is also capable of painting the stars on a <a href="../qtgui/qpaintdevice.html">QPaintDevice</a>, which in this example is either a view or an editor. The <code>myStarCount</code> member variable stores the current rating, and <code>myMaxStarCount</code> stores the highest possible rating (typically 5).</p> <p>The <code>Q_DECLARE_METATYPE()</code> macro makes the type <code>StarRating</code> known to <a href="../qtcore/qvariant.html">QVariant</a>, making it possible to store <code>StarRating</code> values in <a href="../qtcore/qvariant.html">QVariant</a>.</p> <a name="starrating-class-implementation"></a> <h2 id="starrating-class-implementation">StarRating Class Implementation</h2> <p>The constructor initializes <code>myStarCount</code> and <code>myMaxStarCount</code>, and sets up the polygons used to draw stars and diamonds:</p> <pre class="cpp"> StarRating<span class="operator">::</span>StarRating(<span class="type">int</span> starCount<span class="operator">,</span> <span class="type">int</span> maxStarCount) { myStarCount <span class="operator">=</span> starCount; myMaxStarCount <span class="operator">=</span> maxStarCount; starPolygon <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">1.0</span><span class="operator">,</span> <span class="number">0.5</span>); <span class="keyword">for</span> (<span class="type">int</span> i <span class="operator">=</span> <span class="number">1</span>; i <span class="operator"><</span> <span class="number">5</span>; <span class="operator">+</span><span class="operator">+</span>i) starPolygon <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">0.5</span> <span class="operator">+</span> <span class="number">0.5</span> <span class="operator">*</span> std<span class="operator">::</span>cos(<span class="number">0.8</span> <span class="operator">*</span> i <span class="operator">*</span> <span class="number">3.14</span>)<span class="operator">,</span> <span class="number">0.5</span> <span class="operator">+</span> <span class="number">0.5</span> <span class="operator">*</span> std<span class="operator">::</span>sin(<span class="number">0.8</span> <span class="operator">*</span> i <span class="operator">*</span> <span class="number">3.14</span>)); diamondPolygon <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">0.4</span><span class="operator">,</span> <span class="number">0.5</span>) <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">0.5</span><span class="operator">,</span> <span class="number">0.4</span>) <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">0.6</span><span class="operator">,</span> <span class="number">0.5</span>) <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">0.5</span><span class="operator">,</span> <span class="number">0.6</span>) <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="../qtcore/qpointf.html">QPointF</a></span>(<span class="number">0.4</span><span class="operator">,</span> <span class="number">0.5</span>); } </pre> <p>The <code>paint()</code> function paints the stars in this <code>StarRating</code> object on a paint device:</p> <pre class="cpp"> <span class="type">void</span> StarRating<span class="operator">::</span>paint(<span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span> <span class="operator">*</span>painter<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qrect.html">QRect</a></span> <span class="operator">&</span>rect<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtgui/qpalette.html">QPalette</a></span> <span class="operator">&</span>palette<span class="operator">,</span> EditMode mode) <span class="keyword">const</span> { painter<span class="operator">-</span><span class="operator">></span>save(); painter<span class="operator">-</span><span class="operator">></span>setRenderHint(<span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span><span class="operator">::</span>Antialiasing<span class="operator">,</span> <span class="keyword">true</span>); painter<span class="operator">-</span><span class="operator">></span>setPen(<span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>NoPen); <span class="keyword">if</span> (mode <span class="operator">=</span><span class="operator">=</span> Editable) { painter<span class="operator">-</span><span class="operator">></span>setBrush(palette<span class="operator">.</span>highlight()); } <span class="keyword">else</span> { painter<span class="operator">-</span><span class="operator">></span>setBrush(palette<span class="operator">.</span>foreground()); } <span class="type">int</span> yOffset <span class="operator">=</span> (rect<span class="operator">.</span>height() <span class="operator">-</span> PaintingScaleFactor) <span class="operator">/</span> <span class="number">2</span>; painter<span class="operator">-</span><span class="operator">></span>translate(rect<span class="operator">.</span>x()<span class="operator">,</span> rect<span class="operator">.</span>y() <span class="operator">+</span> yOffset); painter<span class="operator">-</span><span class="operator">></span>scale(PaintingScaleFactor<span class="operator">,</span> PaintingScaleFactor); <span class="keyword">for</span> (<span class="type">int</span> i <span class="operator">=</span> <span class="number">0</span>; i <span class="operator"><</span> myMaxStarCount; <span class="operator">+</span><span class="operator">+</span>i) { <span class="keyword">if</span> (i <span class="operator"><</span> myStarCount) { painter<span class="operator">-</span><span class="operator">></span>drawPolygon(starPolygon<span class="operator">,</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>WindingFill); } <span class="keyword">else</span> <span class="keyword">if</span> (mode <span class="operator">=</span><span class="operator">=</span> Editable) { painter<span class="operator">-</span><span class="operator">></span>drawPolygon(diamondPolygon<span class="operator">,</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>WindingFill); } painter<span class="operator">-</span><span class="operator">></span>translate(<span class="number">1.0</span><span class="operator">,</span> <span class="number">0.0</span>); } painter<span class="operator">-</span><span class="operator">></span>restore(); } </pre> <p>We first set the pen and brush we will use for painting. The <code>mode</code> parameter can be either <code>Editable</code> or <code>ReadOnly</code>. If <code>mode</code> is editable, we use the <a href="../qtgui/qpalette.html#ColorRole-enum">Highlight</a> color instead of the <a href="../qtgui/qpalette.html#ColorRole-enum">Foreground</a> color to draw the stars.</p> <p>Then we draw the stars. If we are in <code>Edit</code> mode, we paint diamonds in place of stars if the rating is less than the highest rating.</p> <p>The <code>sizeHint()</code> function returns the preferred size for an area to paint the stars on:</p> <pre class="cpp"> <span class="type"><a href="../qtcore/qsize.html">QSize</a></span> StarRating<span class="operator">::</span>sizeHint() <span class="keyword">const</span> { <span class="keyword">return</span> PaintingScaleFactor <span class="operator">*</span> <span class="type"><a href="../qtcore/qsize.html">QSize</a></span>(myMaxStarCount<span class="operator">,</span> <span class="number">1</span>); } </pre> <p>The preferred size is just enough to paint the maximum number of stars. The function is called by both <code>StarDelegate::sizeHint()</code> and <code>StarEditor::sizeHint()</code>.</p> <a name="the-main-function"></a> <h2 id="the-main-function">The <code>main()</code> Function</h2> <p>Here's the program's <code>main()</code> function:</p> <pre class="cpp"> <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>argv<span class="operator">[</span><span class="operator">]</span>) { <span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv); <span class="type"><a href="qtablewidget.html">QTableWidget</a></span> tableWidget(<span class="number">4</span><span class="operator">,</span> <span class="number">4</span>); tableWidget<span class="operator">.</span>setItemDelegate(<span class="keyword">new</span> StarDelegate); tableWidget<span class="operator">.</span>setEditTriggers(<span class="type"><a href="qabstractitemview.html">QAbstractItemView</a></span><span class="operator">::</span>DoubleClicked <span class="operator">|</span> <span class="type"><a href="qabstractitemview.html">QAbstractItemView</a></span><span class="operator">::</span>SelectedClicked); tableWidget<span class="operator">.</span>setSelectionBehavior(<span class="type"><a href="qabstractitemview.html">QAbstractItemView</a></span><span class="operator">::</span>SelectRows); <span class="type"><a href="../qtcore/qstringlist.html">QStringList</a></span> headerLabels; headerLabels <span class="operator"><</span><span class="operator"><</span> <span class="string">"Title"</span> <span class="operator"><</span><span class="operator"><</span> <span class="string">"Genre"</span> <span class="operator"><</span><span class="operator"><</span> <span class="string">"Artist"</span> <span class="operator"><</span><span class="operator"><</span> <span class="string">"Rating"</span>; tableWidget<span class="operator">.</span>setHorizontalHeaderLabels(headerLabels); populateTableWidget(<span class="operator">&</span>tableWidget); tableWidget<span class="operator">.</span>resizeColumnsToContents(); tableWidget<span class="operator">.</span>resize(<span class="number">500</span><span class="operator">,</span> <span class="number">300</span>); tableWidget<span class="operator">.</span>show(); <span class="keyword">return</span> app<span class="operator">.</span>exec(); } </pre> <p>The <code>main()</code> function creates a <a href="qtablewidget.html">QTableWidget</a> and sets a <code>StarDelegate</code> on it. <a href="qabstractitemview.html#EditTrigger-enum">DoubleClicked</a> and <a href="qabstractitemview.html#EditTrigger-enum">SelectedClicked</a> are set as <a href="qabstractitemview.html#editTriggers-prop">edit triggers</a>, so that the editor is opened with a single click when the star rating item is selected.</p> <p>The <code>populateTableWidget()</code> function fills the <a href="qtablewidget.html">QTableWidget</a> with data:</p> <pre class="cpp"> <span class="type">void</span> populateTableWidget(<span class="type"><a href="qtablewidget.html">QTableWidget</a></span> <span class="operator">*</span>tableWidget) { <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">struct</span> { <span class="keyword">const</span> <span class="type">char</span> <span class="operator">*</span>title; <span class="keyword">const</span> <span class="type">char</span> <span class="operator">*</span>genre; <span class="keyword">const</span> <span class="type">char</span> <span class="operator">*</span>artist; <span class="type">int</span> rating; } staticData<span class="operator">[</span><span class="operator">]</span> <span class="operator">=</span> { { <span class="string">"Mass in B-Minor"</span><span class="operator">,</span> <span class="string">"Baroque"</span><span class="operator">,</span> <span class="string">"J.S. Bach"</span><span class="operator">,</span> <span class="number">5</span> }<span class="operator">,</span> ... { <span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">0</span> } }; <span class="keyword">for</span> (<span class="type">int</span> row <span class="operator">=</span> <span class="number">0</span>; staticData<span class="operator">[</span>row<span class="operator">]</span><span class="operator">.</span>title <span class="operator">!</span><span class="operator">=</span> <span class="number">0</span>; <span class="operator">+</span><span class="operator">+</span>row) { <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span> <span class="operator">*</span>item0 <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span>(staticData<span class="operator">[</span>row<span class="operator">]</span><span class="operator">.</span>title); <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span> <span class="operator">*</span>item1 <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span>(staticData<span class="operator">[</span>row<span class="operator">]</span><span class="operator">.</span>genre); <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span> <span class="operator">*</span>item2 <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span>(staticData<span class="operator">[</span>row<span class="operator">]</span><span class="operator">.</span>artist); <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span> <span class="operator">*</span>item3 <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtablewidgetitem.html">QTableWidgetItem</a></span>; item3<span class="operator">-</span><span class="operator">></span>setData(<span class="number">0</span><span class="operator">,</span> <span class="type"><a href="../qtcore/qvariant.html">QVariant</a></span><span class="operator">::</span>fromValue(StarRating(staticData<span class="operator">[</span>row<span class="operator">]</span><span class="operator">.</span>rating))); tableWidget<span class="operator">-</span><span class="operator">></span>setItem(row<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> item0); tableWidget<span class="operator">-</span><span class="operator">></span>setItem(row<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> item1); tableWidget<span class="operator">-</span><span class="operator">></span>setItem(row<span class="operator">,</span> <span class="number">2</span><span class="operator">,</span> item2); tableWidget<span class="operator">-</span><span class="operator">></span>setItem(row<span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> item3); } } </pre> <p>Notice the call to qVariantFromValue to convert a <code>StarRating</code> to a <a href="../qtcore/qvariant.html">QVariant</a>.</p> <a name="possible-extensions-and-suggestions"></a> <h2 id="possible-extensions-and-suggestions">Possible Extensions and Suggestions</h2> <p>There are many ways to customize Qt's <a href="model-view-programming.html">model/view framework</a>. The approach used in this example is appropriate for most custom delegates and editors. Examples of possibilities not used by the star delegate and star editor are:</p> <ul> <li>It is possible to open editors programmatically by calling <a href="qabstractitemview.html#edit">QAbstractItemView::edit</a>(), instead of relying on edit triggers. This could be used to support other edit triggers than those offered by the <a href="qabstractitemview.html#EditTrigger-enum">QAbstractItemView::EditTrigger</a> enum. For example, in the Star Delegate example, hovering over an item with the mouse might make sense as a way to pop up an editor.</li> <li>By reimplementing <a href="qabstractitemdelegate.html#editorEvent">QAbstractItemDelegate::editorEvent</a>(), it is possible to implement the editor directly in the delegate, instead of creating a separate <a href="qwidget.html">QWidget</a> subclass.</li> </ul> <p>Files:</p> <ul> <li><a href="qtwidgets-itemviews-stardelegate-main-cpp.html">itemviews/stardelegate/main.cpp</a></li> <li><a href="qtwidgets-itemviews-stardelegate-stardelegate-cpp.html">itemviews/stardelegate/stardelegate.cpp</a></li> <li><a href="qtwidgets-itemviews-stardelegate-stardelegate-h.html">itemviews/stardelegate/stardelegate.h</a></li> <li><a href="qtwidgets-itemviews-stardelegate-stardelegate-pro.html">itemviews/stardelegate/stardelegate.pro</a></li> <li><a href="qtwidgets-itemviews-stardelegate-stareditor-cpp.html">itemviews/stardelegate/stareditor.cpp</a></li> <li><a href="qtwidgets-itemviews-stardelegate-stareditor-h.html">itemviews/stardelegate/stareditor.h</a></li> <li><a href="qtwidgets-itemviews-stardelegate-starrating-cpp.html">itemviews/stardelegate/starrating.cpp</a></li> <li><a href="qtwidgets-itemviews-stardelegate-starrating-h.html">itemviews/stardelegate/starrating.h</a></li> </ul> </div> <!-- @@@itemviews/stardelegate --> </div> </div> </div> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2019 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners.<br/> The documentation provided herein is licensed under the terms of the <a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation License version 1.3</a> as published by the Free Software Foundation.<br/> Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners. </p> </div> </body> </html>