<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- elidedlabel.qdoc --> <title>Elided Label Example | Qt Widgets 5.9</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 5.9</td><td ><a href="qtwidgets-index.html">Qt Widgets</a></td><td >Elided Label Example</td></tr></table><table class="buildversion"><tr> <td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</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="#elidedlabel-class-definition">ElidedLabel Class Definition</a></li> <li class="level1"><a href="#elidedlabel-class-implementation">ElidedLabel Class Implementation</a></li> <li class="level1"><a href="#testwidget-class-definition">TestWidget Class Definition</a></li> <li class="level1"><a href="#testwidget-class-implementation">TestWidget Class Implementation</a></li> <li class="level1"><a href="#the-main-function">The <code>main()</code> Function</a></li> </ul> </div> <div class="sidebar-content" id="sidebar-content"></div></div> <h1 class="title">Elided Label Example</h1> <span class="subtitle"></span> <!-- $$$widgets/elidedlabel-description --> <div class="descr"> <a name="details"></a> <p class="centerAlign"><img src="images/elidedlabel-example.png" alt="Elided Label example on XPressMusic 5800" /></p><p>When text of varying length has to be displayed in a uniformly sized area, for instance within a list or grid view where all list items have the same size, it can be useful to give the user a visual clue when not all text is visible. <a href="qlabel.html">QLabel</a> can elide text that doesn't fit within it, but only in one line. The <code>ElidedLabel</code> widget shown in this example word wraps its text by its width, and elides the last visible line if some text is left out. <code>TestWidget</code> gives control to the features of <code>ElidedWidget</code> and forms the example application.</p> <a name="elidedlabel-class-definition"></a> <h2 id="elidedlabel-class-definition">ElidedLabel Class Definition</h2> <p>Like <a href="qlabel.html">QLabel</a>, <code>ElidedLabel</code> inherits from <a href="qframe.html">QFrame</a>. Here's the definition of the <code>ElidedLabel</code> class:</p> <pre class="cpp"> <span class="keyword">class</span> ElidedLabel : <span class="keyword">public</span> <span class="type"><a href="qframe.html">QFrame</a></span> { Q_OBJECT Q_PROPERTY(<span class="type"><a href="../qtcore/qstring.html">QString</a></span> text READ text WRITE setText) Q_PROPERTY(bool isElided READ isElided) <span class="keyword">public</span>: <span class="keyword">explicit</span> ElidedLabel(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>text<span class="operator">,</span> <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">void</span> setText(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>text); <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span> text() <span class="keyword">const</span> { <span class="keyword">return</span> content; } bool isElided() <span class="keyword">const</span> { <span class="keyword">return</span> elided; } <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="keyword">signals</span>: <span class="type">void</span> elisionChanged(bool elided); <span class="keyword">private</span>: bool elided; <span class="type"><a href="../qtcore/qstring.html">QString</a></span> content; }; </pre> <p>The <code>isElided</code> property depends the font, text content and geometry of the widget. Whenever any of these change, the <code>elisionChanged()</code> signal might trigger. We cache the current elision value in <code>elided</code>, so that it doesn't have to be recomputed every time it's asked for.</p> <a name="elidedlabel-class-implementation"></a> <h2 id="elidedlabel-class-implementation">ElidedLabel Class Implementation</h2> <p>Except for initializing the member variables, the constructor sets the size policy to be horizontally expanding, since it's meant to fill the width of its container and grow vertically.</p> <pre class="cpp"> ElidedLabel<span class="operator">::</span>ElidedLabel(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>text<span class="operator">,</span> <span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent) : <span class="type"><a href="qframe.html">QFrame</a></span>(parent) <span class="operator">,</span> elided(<span class="keyword">false</span>) <span class="operator">,</span> content(text) { setSizePolicy(<span class="type"><a href="qsizepolicy.html">QSizePolicy</a></span><span class="operator">::</span>Expanding<span class="operator">,</span> <span class="type"><a href="qsizepolicy.html">QSizePolicy</a></span><span class="operator">::</span>Preferred); } </pre> <p>Changing the <code>content</code> require a repaint of the widget.</p> <pre class="cpp"> <span class="type">void</span> ElidedLabel<span class="operator">::</span>setText(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>newText) { content <span class="operator">=</span> newText; update(); } </pre> <p><a href="../qtgui/qtextlayout.html">QTextLayout</a> is used in the <code>paintEvent()</code> to divide the <code>content</code> into lines, that wrap on word boundaries. Each line, except the last visible one, is drawn <code>lineSpacing</code> pixels below the previous one. The <code>draw()</code> method of <a href="../qtgui/qtextline.html">QTextLine</a> will draw the line using the coordinate point as the top left corner.</p> <pre class="cpp"> <span class="type">void</span> ElidedLabel<span class="operator">::</span>paintEvent(<span class="type"><a href="../qtgui/qpaintevent.html">QPaintEvent</a></span> <span class="operator">*</span>event) { <span class="type"><a href="qframe.html">QFrame</a></span><span class="operator">::</span>paintEvent(event); <span class="type"><a href="../qtgui/qpainter.html">QPainter</a></span> painter(<span class="keyword">this</span>); <span class="type"><a href="../qtgui/qfontmetrics.html">QFontMetrics</a></span> fontMetrics <span class="operator">=</span> painter<span class="operator">.</span>fontMetrics(); bool didElide <span class="operator">=</span> <span class="keyword">false</span>; <span class="type">int</span> lineSpacing <span class="operator">=</span> fontMetrics<span class="operator">.</span>lineSpacing(); <span class="type">int</span> y <span class="operator">=</span> <span class="number">0</span>; <span class="type"><a href="../qtgui/qtextlayout.html">QTextLayout</a></span> textLayout(content<span class="operator">,</span> painter<span class="operator">.</span>font()); textLayout<span class="operator">.</span>beginLayout(); forever { <span class="type"><a href="../qtgui/qtextline.html">QTextLine</a></span> line <span class="operator">=</span> textLayout<span class="operator">.</span>createLine(); <span class="keyword">if</span> (<span class="operator">!</span>line<span class="operator">.</span>isValid()) <span class="keyword">break</span>; line<span class="operator">.</span>setLineWidth(width()); <span class="type">int</span> nextLineY <span class="operator">=</span> y <span class="operator">+</span> lineSpacing; <span class="keyword">if</span> (height() <span class="operator">></span><span class="operator">=</span> nextLineY <span class="operator">+</span> lineSpacing) { line<span class="operator">.</span>draw(<span class="operator">&</span>painter<span class="operator">,</span> <span class="type"><a href="../qtcore/qpoint.html">QPoint</a></span>(<span class="number">0</span><span class="operator">,</span> y)); y <span class="operator">=</span> nextLineY; </pre> <p>Unfortunately, <a href="../qtgui/qtextlayout.html">QTextLayout</a> does not elide text, so the last visible line has to be treated differently. This last line is elided if it is too wide. The <code>drawText()</code> method of <a href="../qtgui/qpainter.html">QPainter</a> draws the text starting from the base line, which is <code>ascecnt()</code> pixels below the last drawn line.</p> <p>Finally, one more line is created to see if everything fit on this line.</p> <pre class="cpp"> } <span class="keyword">else</span> { <span class="type"><a href="../qtcore/qstring.html">QString</a></span> lastLine <span class="operator">=</span> content<span class="operator">.</span>mid(line<span class="operator">.</span>textStart()); <span class="type"><a href="../qtcore/qstring.html">QString</a></span> elidedLastLine <span class="operator">=</span> fontMetrics<span class="operator">.</span>elidedText(lastLine<span class="operator">,</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>ElideRight<span class="operator">,</span> width()); painter<span class="operator">.</span>drawText(<span class="type"><a href="../qtcore/qpoint.html">QPoint</a></span>(<span class="number">0</span><span class="operator">,</span> y <span class="operator">+</span> fontMetrics<span class="operator">.</span>ascent())<span class="operator">,</span> elidedLastLine); line <span class="operator">=</span> textLayout<span class="operator">.</span>createLine(); didElide <span class="operator">=</span> line<span class="operator">.</span>isValid(); <span class="keyword">break</span>; } } textLayout<span class="operator">.</span>endLayout(); </pre> <p>If the text was elided and wasn't before or vice versa, cache it in <code>elided</code> and emit the change.</p> <pre class="cpp"> <span class="keyword">if</span> (didElide <span class="operator">!</span><span class="operator">=</span> elided) { elided <span class="operator">=</span> didElide; <span class="keyword">emit</span> elisionChanged(didElide); } } </pre> <a name="testwidget-class-definition"></a> <h2 id="testwidget-class-definition">TestWidget Class Definition</h2> <p><code>TestWidget</code> is a <a href="qwidget.html">QWidget</a> and is the main window of the example. It contains an <code>ElidedLabel</code> which can be resized with two <a href="qslider.html">QSlider</a> widgets.</p> <pre class="cpp"> <span class="keyword">class</span> TestWidget : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span> { Q_OBJECT <span class="keyword">public</span>: TestWidget(<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="keyword">protected</span>: <span class="type">void</span> resizeEvent(<span class="type"><a href="../qtgui/qresizeevent.html">QResizeEvent</a></span> <span class="operator">*</span>event) override; <span class="keyword">private</span> <span class="keyword">slots</span>: <span class="type">void</span> switchText(); <span class="type">void</span> onWidthChanged(<span class="type">int</span> width); <span class="type">void</span> onHeightChanged(<span class="type">int</span> height); <span class="keyword">private</span>: <span class="type">int</span> sampleIndex; <span class="type"><a href="../qtcore/qstringlist.html">QStringList</a></span> textSamples; ElidedLabel <span class="operator">*</span>elidedText; <span class="type"><a href="qslider.html">QSlider</a></span> <span class="operator">*</span>heightSlider; <span class="type"><a href="qslider.html">QSlider</a></span> <span class="operator">*</span>widthSlider; }; </pre> <a name="testwidget-class-implementation"></a> <h2 id="testwidget-class-implementation">TestWidget Class Implementation</h2> <p>The constructor initializes the whole widget. Strings of different length are stored in <code>textSamples</code>. The user is able to switch between these.</p> <pre class="cpp"> TestWidget<span class="operator">::</span>TestWidget(<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) { <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> romeo <span class="operator">=</span> tr( <span class="string">"But soft, what light through yonder window breaks? / "</span> <span class="string">"It is the east, and Juliet is the sun. / "</span> <span class="string">"Arise, fair sun, and kill the envious moon, / "</span> <span class="string">"Who is already sick and pale with grief / "</span> <span class="string">"That thou, her maid, art far more fair than she."</span> ); <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> macbeth <span class="operator">=</span> tr( <span class="string">"To-morrow, and to-morrow, and to-morrow, / "</span> <span class="string">"Creeps in this petty pace from day to day, / "</span> <span class="string">"To the last syllable of recorded time; / "</span> <span class="string">"And all our yesterdays have lighted fools / "</span> <span class="string">"The way to dusty death. Out, out, brief candle! / "</span> <span class="string">"Life's but a walking shadow, a poor player, / "</span> <span class="string">"That struts and frets his hour upon the stage, / "</span> <span class="string">"And then is heard no more. It is a tale / "</span> <span class="string">"Told by an idiot, full of sound and fury, / "</span> <span class="string">"Signifying nothing."</span> ); <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> harry <span class="operator">=</span> tr(<span class="string">"Feeling lucky, punk?"</span>); textSamples <span class="operator"><</span><span class="operator"><</span> romeo <span class="operator"><</span><span class="operator"><</span> macbeth <span class="operator"><</span><span class="operator"><</span> harry; </pre> <p>An <code>ElidedLabel</code> is created to contain the first of the sample strings. The frame is made visible to make it easier to see the actual size of the widget.</p> <pre class="cpp"> sampleIndex <span class="operator">=</span> <span class="number">0</span>; elidedText <span class="operator">=</span> <span class="keyword">new</span> ElidedLabel(textSamples<span class="operator">[</span>sampleIndex<span class="operator">]</span><span class="operator">,</span> <span class="keyword">this</span>); elidedText<span class="operator">-</span><span class="operator">></span>setFrameStyle(<span class="type"><a href="qframe.html">QFrame</a></span><span class="operator">::</span>Box); </pre> <p>The buttons and the elision label are created. By connecting the <code>elisionChanged()</code> signal to the <code>setVisible()</code> slot of the <code>label</code>, it will act as an indicator to when the text is elided or not. This signal could, for instance, be used to make a "More" button visible, or similar.</p> <pre class="cpp"> <span class="type"><a href="qpushbutton.html">QPushButton</a></span> <span class="operator">*</span>switchButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpushbutton.html">QPushButton</a></span>(tr(<span class="string">"Switch text"</span>)); connect(switchButton<span class="operator">,</span> SIGNAL(clicked(bool))<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(switchText())); <span class="type"><a href="qpushbutton.html">QPushButton</a></span> <span class="operator">*</span>exitButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpushbutton.html">QPushButton</a></span>(tr(<span class="string">"Exit"</span>)); connect(exitButton<span class="operator">,</span> SIGNAL(clicked(bool))<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(close())); <span class="type"><a href="qlabel.html">QLabel</a></span> <span class="operator">*</span>label <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qlabel.html">QLabel</a></span>(tr(<span class="string">"Elided"</span>)); label<span class="operator">-</span><span class="operator">></span>setVisible(elidedText<span class="operator">-</span><span class="operator">></span>isElided()); connect(elidedText<span class="operator">,</span> SIGNAL(elisionChanged(bool))<span class="operator">,</span> label<span class="operator">,</span> SLOT(setVisible(bool))); </pre> <p>The <code>widthSlider</code> and <code>heightSlider</code> specify the size of the <code>elidedText</code>. Since the y-axis is inverted, the <code>heightSlider</code> has to be inverted to act appropriately.</p> <pre class="cpp"> widthSlider <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qslider.html">QSlider</a></span>(<span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>Horizontal); widthSlider<span class="operator">-</span><span class="operator">></span>setMinimum(<span class="number">0</span>); connect(widthSlider<span class="operator">,</span> SIGNAL(valueChanged(<span class="type">int</span>))<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(onWidthChanged(<span class="type">int</span>))); heightSlider <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qslider.html">QSlider</a></span>(<span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>Vertical); heightSlider<span class="operator">-</span><span class="operator">></span>setInvertedAppearance(<span class="keyword">true</span>); heightSlider<span class="operator">-</span><span class="operator">></span>setMinimum(<span class="number">0</span>); connect(heightSlider<span class="operator">,</span> SIGNAL(valueChanged(<span class="type">int</span>))<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(onHeightChanged(<span class="type">int</span>))); </pre> <p>The components are all stored in a <a href="qgridlayout.html">QGridLayout</a>, which is made the layout of the <code>TestWidget</code>.</p> <pre class="cpp"> <span class="type"><a href="qgridlayout.html">QGridLayout</a></span> <span class="operator">*</span>layout <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qgridlayout.html">QGridLayout</a></span>(); layout<span class="operator">-</span><span class="operator">></span>addWidget(label<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>AlignCenter); layout<span class="operator">-</span><span class="operator">></span>addWidget(switchButton<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">2</span>); layout<span class="operator">-</span><span class="operator">></span>addWidget(exitButton<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">3</span>); layout<span class="operator">-</span><span class="operator">></span>addWidget(widthSlider<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">3</span>); layout<span class="operator">-</span><span class="operator">></span>addWidget(heightSlider<span class="operator">,</span> <span class="number">2</span><span class="operator">,</span> <span class="number">0</span>); layout<span class="operator">-</span><span class="operator">></span>addWidget(elidedText<span class="operator">,</span> <span class="number">2</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>AlignTop <span class="operator">|</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>AlignLeft); setLayout(layout); </pre> <p>The <code>widthSlider</code> and <code>heightSlider</code> have the exact same length as the dimensions of the <code>elidedText</code>. The maximum value for both of them is thus their lengths, and each tick indicates one pixel.</p> <pre class="cpp"> <span class="type">void</span> TestWidget<span class="operator">::</span>resizeEvent(<span class="type"><a href="../qtgui/qresizeevent.html">QResizeEvent</a></span> <span class="operator">*</span>event) { Q_UNUSED(event) <span class="type">int</span> maxWidth <span class="operator">=</span> widthSlider<span class="operator">-</span><span class="operator">></span>width(); widthSlider<span class="operator">-</span><span class="operator">></span>setMaximum(maxWidth); widthSlider<span class="operator">-</span><span class="operator">></span>setValue(maxWidth <span class="operator">/</span> <span class="number">2</span>); <span class="type">int</span> maxHeight <span class="operator">=</span> heightSlider<span class="operator">-</span><span class="operator">></span>height(); heightSlider<span class="operator">-</span><span class="operator">></span>setMaximum(maxHeight); heightSlider<span class="operator">-</span><span class="operator">></span>setValue(maxHeight <span class="operator">/</span> <span class="number">2</span>); elidedText<span class="operator">-</span><span class="operator">></span>setFixedSize(widthSlider<span class="operator">-</span><span class="operator">></span>value()<span class="operator">,</span> heightSlider<span class="operator">-</span><span class="operator">></span>value()); } </pre> <p>The <code>switchText()</code> slot simply cycles through all the available sample texts.</p> <pre class="cpp"> <span class="type">void</span> TestWidget<span class="operator">::</span>switchText() { sampleIndex <span class="operator">=</span> (sampleIndex <span class="operator">+</span> <span class="number">1</span>) <span class="operator">%</span> textSamples<span class="operator">.</span>size(); elidedText<span class="operator">-</span><span class="operator">></span>setText(textSamples<span class="operator">.</span>at(sampleIndex)); } </pre> <p>These slots set the width and height of the <code>elided</code> text, in response to changes in the sliders.</p> <a name="the-main-function"></a> <h2 id="the-main-function">The <code>main()</code> Function</h2> <p>The <code>main()</code> function creates an instance of <code>TestWidget</code> fullscreen and enters the message loop.</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> application( argc<span class="operator">,</span> argv ); TestWidget w; w<span class="operator">.</span>showFullScreen(); <span class="keyword">return</span> application<span class="operator">.</span>exec(); } </pre> <p>Files:</p> <ul> <li><a href="qtwidgets-widgets-elidedlabel-elidedlabel-cpp.html">widgets/elidedlabel/elidedlabel.cpp</a></li> <li><a href="qtwidgets-widgets-elidedlabel-elidedlabel-h.html">widgets/elidedlabel/elidedlabel.h</a></li> <li><a href="qtwidgets-widgets-elidedlabel-testwidget-cpp.html">widgets/elidedlabel/testwidget.cpp</a></li> <li><a href="qtwidgets-widgets-elidedlabel-testwidget-h.html">widgets/elidedlabel/testwidget.h</a></li> <li><a href="qtwidgets-widgets-elidedlabel-main-cpp.html">widgets/elidedlabel/main.cpp</a></li> <li><a href="qtwidgets-widgets-elidedlabel-elidedlabel-pro.html">widgets/elidedlabel/elidedlabel.pro</a></li> </ul> </div> <!-- @@@widgets/elidedlabel --> </div> </div> </div> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2017 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>