<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- qlayoutitem.cpp --> <title>QLayoutItem Class | 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="qtwidgets-module.html">C++ Classes</a></td><td >QLayoutItem</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="#public-functions">Public Functions</a></li> <li class="level1"><a href="#protected-variables">Protected Variables</a></li> <li class="level1"><a href="#details">Detailed Description</a></li> </ul> </div> <div class="sidebar-content" id="sidebar-content"></div></div> <h1 class="title">QLayoutItem Class</h1> <!-- $$$QLayoutItem-brief --> <p>The <a href="qlayoutitem.html">QLayoutItem</a> class provides an abstract item that a <a href="qlayout.html">QLayout</a> manipulates. <a href="#details">More...</a></p> <!-- @@@QLayoutItem --> <div class="table"><table class="alignedsummary"> <tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QLayoutItem></span> </td></tr><tr><td class="memItemLeft rightAlign topAlign"> qmake:</td><td class="memItemRight bottomAlign"> QT += widgets</td></tr><tr><td class="memItemLeft rightAlign topAlign"> Inherited By:</td><td class="memItemRight bottomAlign"> <p><a href="qlayout.html">QLayout</a>, <a href="qspaceritem.html">QSpacerItem</a>, and <a href="qwidgetitem.html">QWidgetItem</a></p> </td></tr></table></div><ul> <li><a href="qlayoutitem-members.html">List of all members, including inherited members</a></li> </ul> <a name="public-functions"></a> <h2 id="public-functions">Public Functions</h2> <div class="table"><table class="alignedsummary"> <tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#QLayoutItem">QLayoutItem</a></b>(Qt::Alignment <i>alignment</i> = ...)</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#dtor.QLayoutItem">~QLayoutItem</a></b>()</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> Qt::Alignment </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#alignment">alignment</a></b>() const</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QSizePolicy::ControlTypes </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#controlTypes">controlTypes</a></b>() const</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual Qt::Orientations </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#expandingDirections">expandingDirections</a></b>() const = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QRect </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#geometry">geometry</a></b>() const = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual bool </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#hasHeightForWidth">hasHeightForWidth</a></b>() const</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual int </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#heightForWidth">heightForWidth</a></b>(<i>int</i>) const</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual void </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#invalidate">invalidate</a></b>()</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual bool </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#isEmpty">isEmpty</a></b>() const = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QLayout *</td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#layout">layout</a></b>()</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QSize </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#maximumSize">maximumSize</a></b>() const = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual int </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#minimumHeightForWidth">minimumHeightForWidth</a></b>(int <i>w</i>) const</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QSize </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#minimumSize">minimumSize</a></b>() const = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#setAlignment">setAlignment</a></b>(Qt::Alignment <i>alignment</i>)</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual void </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#setGeometry">setGeometry</a></b>(const QRect &<i>r</i>) = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QSize </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#sizeHint">sizeHint</a></b>() const = 0</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QSpacerItem *</td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#spacerItem">spacerItem</a></b>()</td></tr> <tr><td class="memItemLeft rightAlign topAlign"> virtual QWidget *</td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#widget">widget</a></b>()</td></tr> </table></div> <a name="protected-variables"></a> <h2 id="protected-variables">Protected Variables</h2> <div class="table"><table class="alignedsummary"> <tr><td class="memItemLeft rightAlign topAlign"> Qt::Alignment </td><td class="memItemRight bottomAlign"><b><a href="qlayoutitem.html#align-var">align</a></b></td></tr> </table></div> <a name="details"></a> <!-- $$$QLayoutItem-description --> <div class="descr"> <h2 id="details">Detailed Description</h2> <p>The <a href="qlayoutitem.html">QLayoutItem</a> class provides an abstract item that a <a href="qlayout.html">QLayout</a> manipulates.</p> <p>This is used by custom layouts.</p> <p>Pure virtual functions are provided to return information about the layout, including, <a href="qlayoutitem.html#sizeHint">sizeHint</a>(), <a href="qlayoutitem.html#minimumSize">minimumSize</a>(), <a href="qlayoutitem.html#maximumSize">maximumSize</a>() and expanding().</p> <p>The layout's geometry can be set and retrieved with <a href="qlayoutitem.html#setGeometry">setGeometry</a>() and <a href="qlayoutitem.html#geometry">geometry</a>(), and its alignment with <a href="qlayoutitem.html#setAlignment">setAlignment</a>() and <a href="qlayoutitem.html#alignment">alignment</a>().</p> <p><a href="qlayoutitem.html#isEmpty">isEmpty</a>() returns whether the layout item is empty. If the concrete item is a <a href="qwidget.html">QWidget</a>, it can be retrieved using <a href="qlayoutitem.html#widget">widget</a>(). Similarly for <a href="qlayoutitem.html#layout">layout</a>() and <a href="qlayoutitem.html#spacerItem">spacerItem</a>().</p> <p>Some layouts have width and height interdependencies. These can be expressed using <a href="qlayoutitem.html#hasHeightForWidth">hasHeightForWidth</a>(), <a href="qlayoutitem.html#heightForWidth">heightForWidth</a>(), and <a href="qlayoutitem.html#minimumHeightForWidth">minimumHeightForWidth</a>(). For more explanation see the <i>Qt Quarterly</i> article <a href="http://doc.qt.io/archives/qq/qq04-height-for-width.html">Trading Height for Width</a>.</p> </div> <p><b>See also </b><a href="qlayout.html">QLayout</a>.</p> <!-- @@@QLayoutItem --> <div class="func"> <h2>Member Function Documentation</h2> <!-- $$$QLayoutItem[overload1]$$$QLayoutItemQt::Alignment --> <h3 class="fn" id="QLayoutItem"><a name="QLayoutItem"></a>QLayoutItem::<span class="name">QLayoutItem</span>(<span class="type"><a href="../qtcore/qt.html#AlignmentFlag-enum">Qt::Alignment</a></span> <i>alignment</i> = ...)</h3> <p>Constructs a layout item with an <i>alignment</i>. Not all subclasses support alignment.</p> <!-- @@@QLayoutItem --> <!-- $$$~QLayoutItem[overload1]$$$~QLayoutItem --> <h3 class="fn" id="dtor.QLayoutItem"><a name="dtor.QLayoutItem"></a><code>[virtual] </code>QLayoutItem::<span class="name">~QLayoutItem</span>()</h3> <p>Destroys the <a href="qlayoutitem.html">QLayoutItem</a>.</p> <!-- @@@~QLayoutItem --> <!-- $$$alignment[overload1]$$$alignment --> <h3 class="fn" id="alignment"><a name="alignment"></a><span class="type"><a href="../qtcore/qt.html#AlignmentFlag-enum">Qt::Alignment</a></span> QLayoutItem::<span class="name">alignment</span>() const</h3> <p>Returns the alignment of this item.</p> <p><b>See also </b><a href="qlayoutitem.html#setAlignment">setAlignment</a>().</p> <!-- @@@alignment --> <!-- $$$controlTypes[overload1]$$$controlTypes --> <h3 class="fn" id="controlTypes"><a name="controlTypes"></a><code>[virtual] </code><span class="type"><a href="qsizepolicy.html#ControlType-enum">QSizePolicy::ControlTypes</a></span> QLayoutItem::<span class="name">controlTypes</span>() const</h3> <p>Returns the control type(s) for the layout item. For a <a href="qwidgetitem.html">QWidgetItem</a>, the control type comes from the widget's size policy; for a <a href="qlayoutitem.html">QLayoutItem</a>, the control types is derived from the layout's contents.</p> <p><b>See also </b><a href="qsizepolicy.html#controlType">QSizePolicy::controlType</a>().</p> <!-- @@@controlTypes --> <!-- $$$expandingDirections[overload1]$$$expandingDirections --> <h3 class="fn" id="expandingDirections"><a name="expandingDirections"></a><code>[pure virtual] </code><span class="type"><a href="../qtcore/qt.html#Orientation-enum">Qt::Orientations</a></span> QLayoutItem::<span class="name">expandingDirections</span>() const</h3> <p>Returns whether this layout item can make use of more space than <a href="qlayoutitem.html#sizeHint">sizeHint</a>(). A value of <a href="../qtcore/qt.html#Orientation-enum">Qt::Vertical</a> or <a href="../qtcore/qt.html#Orientation-enum">Qt::Horizontal</a> means that it wants to grow in only one dimension, whereas <a href="../qtcore/qt.html#Orientation-enum">Qt::Vertical</a> | <a href="../qtcore/qt.html#Orientation-enum">Qt::Horizontal</a> means that it wants to grow in both dimensions.</p> <!-- @@@expandingDirections --> <!-- $$$geometry[overload1]$$$geometry --> <h3 class="fn" id="geometry"><a name="geometry"></a><code>[pure virtual] </code><span class="type"><a href="../qtcore/qrect.html">QRect</a></span> QLayoutItem::<span class="name">geometry</span>() const</h3> <p>Returns the rectangle covered by this layout item.</p> <p><b>See also </b><a href="qlayoutitem.html#setGeometry">setGeometry</a>().</p> <!-- @@@geometry --> <!-- $$$hasHeightForWidth[overload1]$$$hasHeightForWidth --> <h3 class="fn" id="hasHeightForWidth"><a name="hasHeightForWidth"></a><code>[virtual] </code><span class="type">bool</span> QLayoutItem::<span class="name">hasHeightForWidth</span>() const</h3> <p>Returns <code>true</code> if this layout's preferred height depends on its width; otherwise returns <code>false</code>. The default implementation returns false.</p> <p>Reimplement this function in layout managers that support height for width.</p> <p><b>See also </b><a href="qlayoutitem.html#heightForWidth">heightForWidth</a>() and <a href="qwidget.html#heightForWidth">QWidget::heightForWidth</a>().</p> <!-- @@@hasHeightForWidth --> <!-- $$$heightForWidth[overload1]$$$heightForWidthint --> <h3 class="fn" id="heightForWidth"><a name="heightForWidth"></a><code>[virtual] </code><span class="type">int</span> QLayoutItem::<span class="name">heightForWidth</span>(<i>int</i>) const</h3> <p>Returns the preferred height for this layout item, given the width, which is not used in this default implementation.</p> <p>The default implementation returns -1, indicating that the preferred height is independent of the width of the item. Using the function <a href="qlayoutitem.html#hasHeightForWidth">hasHeightForWidth</a>() will typically be much faster than calling this function and testing for -1.</p> <p>Reimplement this function in layout managers that support height for width. A typical implementation will look like this:</p> <pre class="cpp"> <span class="type">int</span> MyLayout<span class="operator">::</span>heightForWidth(<span class="type">int</span> w) <span class="keyword">const</span> { <span class="keyword">if</span> (cache_dirty <span class="operator">|</span><span class="operator">|</span> cached_width <span class="operator">!</span><span class="operator">=</span> w) { <span class="comment">// not all C++ compilers support "mutable"</span> MyLayout <span class="operator">*</span>that <span class="operator">=</span> (MyLayout<span class="operator">*</span>)<span class="keyword">this</span>; <span class="type">int</span> h <span class="operator">=</span> calculateHeightForWidth(w); that<span class="operator">-</span><span class="operator">></span>cached_hfw <span class="operator">=</span> h; <span class="keyword">return</span> h; } <span class="keyword">return</span> cached_hfw; } </pre> <p>Caching is strongly recommended; without it layout will take exponential time.</p> <p><b>See also </b><a href="qlayoutitem.html#hasHeightForWidth">hasHeightForWidth</a>().</p> <!-- @@@heightForWidth --> <!-- $$$invalidate[overload1]$$$invalidate --> <h3 class="fn" id="invalidate"><a name="invalidate"></a><code>[virtual] </code><span class="type">void</span> QLayoutItem::<span class="name">invalidate</span>()</h3> <p>Invalidates any cached information in this layout item.</p> <!-- @@@invalidate --> <!-- $$$isEmpty[overload1]$$$isEmpty --> <h3 class="fn" id="isEmpty"><a name="isEmpty"></a><code>[pure virtual] </code><span class="type">bool</span> QLayoutItem::<span class="name">isEmpty</span>() const</h3> <p>Implemented in subclasses to return whether this item is empty, i.e. whether it contains any widgets.</p> <!-- @@@isEmpty --> <!-- $$$layout[overload1]$$$layout --> <h3 class="fn" id="layout"><a name="layout"></a><code>[virtual] </code><span class="type"><a href="qlayout.html">QLayout</a></span> *QLayoutItem::<span class="name">layout</span>()</h3> <p>If this item is a <a href="qlayout.html">QLayout</a>, it is returned as a <a href="qlayout.html">QLayout</a>; otherwise 0 is returned. This function provides type-safe casting.</p> <p><b>See also </b><a href="qlayoutitem.html#spacerItem">spacerItem</a>() and <a href="qlayoutitem.html#widget">widget</a>().</p> <!-- @@@layout --> <!-- $$$maximumSize[overload1]$$$maximumSize --> <h3 class="fn" id="maximumSize"><a name="maximumSize"></a><code>[pure virtual] </code><span class="type"><a href="../qtcore/qsize.html">QSize</a></span> QLayoutItem::<span class="name">maximumSize</span>() const</h3> <p>Implemented in subclasses to return the maximum size of this item.</p> <!-- @@@maximumSize --> <!-- $$$minimumHeightForWidth[overload1]$$$minimumHeightForWidthint --> <h3 class="fn" id="minimumHeightForWidth"><a name="minimumHeightForWidth"></a><code>[virtual] </code><span class="type">int</span> QLayoutItem::<span class="name">minimumHeightForWidth</span>(<span class="type">int</span> <i>w</i>) const</h3> <p>Returns the minimum height this widget needs for the given width, <i>w</i>. The default implementation simply returns <a href="qlayoutitem.html#heightForWidth">heightForWidth</a>(<i>w</i>).</p> <!-- @@@minimumHeightForWidth --> <!-- $$$minimumSize[overload1]$$$minimumSize --> <h3 class="fn" id="minimumSize"><a name="minimumSize"></a><code>[pure virtual] </code><span class="type"><a href="../qtcore/qsize.html">QSize</a></span> QLayoutItem::<span class="name">minimumSize</span>() const</h3> <p>Implemented in subclasses to return the minimum size of this item.</p> <!-- @@@minimumSize --> <!-- $$$setAlignment[overload1]$$$setAlignmentQt::Alignment --> <h3 class="fn" id="setAlignment"><a name="setAlignment"></a><span class="type">void</span> QLayoutItem::<span class="name">setAlignment</span>(<span class="type"><a href="../qtcore/qt.html#AlignmentFlag-enum">Qt::Alignment</a></span> <i>alignment</i>)</h3> <p>Sets the alignment of this item to <i>alignment</i>.</p> <p><b>Note:</b> Item alignment is only supported by <a href="qlayoutitem.html">QLayoutItem</a> subclasses where it would have a visual effect. Except for <a href="qspaceritem.html">QSpacerItem</a>, which provides blank space for layouts, all public Qt classes that inherit <a href="qlayoutitem.html">QLayoutItem</a> support item alignment.</p> <p><b>See also </b><a href="qlayoutitem.html#alignment">alignment</a>().</p> <!-- @@@setAlignment --> <!-- $$$setGeometry[overload1]$$$setGeometryconstQRect& --> <h3 class="fn" id="setGeometry"><a name="setGeometry"></a><code>[pure virtual] </code><span class="type">void</span> QLayoutItem::<span class="name">setGeometry</span>(const <span class="type"><a href="../qtcore/qrect.html">QRect</a></span> &<i>r</i>)</h3> <p>Implemented in subclasses to set this item's geometry to <i>r</i>.</p> <p><b>See also </b><a href="qlayoutitem.html#geometry">geometry</a>().</p> <!-- @@@setGeometry --> <!-- $$$sizeHint[overload1]$$$sizeHint --> <h3 class="fn" id="sizeHint"><a name="sizeHint"></a><code>[pure virtual] </code><span class="type"><a href="../qtcore/qsize.html">QSize</a></span> QLayoutItem::<span class="name">sizeHint</span>() const</h3> <p>Implemented in subclasses to return the preferred size of this item.</p> <!-- @@@sizeHint --> <!-- $$$spacerItem[overload1]$$$spacerItem --> <h3 class="fn" id="spacerItem"><a name="spacerItem"></a><code>[virtual] </code><span class="type"><a href="qspaceritem.html">QSpacerItem</a></span> *QLayoutItem::<span class="name">spacerItem</span>()</h3> <p>If this item is a <a href="qspaceritem.html">QSpacerItem</a>, it is returned as a <a href="qspaceritem.html">QSpacerItem</a>; otherwise 0 is returned. This function provides type-safe casting.</p> <p><b>See also </b><a href="qlayoutitem.html#layout">layout</a>() and <a href="qlayoutitem.html#widget">widget</a>().</p> <!-- @@@spacerItem --> <!-- $$$widget[overload1]$$$widget --> <h3 class="fn" id="widget"><a name="widget"></a><code>[virtual] </code><span class="type"><a href="qwidget.html">QWidget</a></span> *QLayoutItem::<span class="name">widget</span>()</h3> <p>If this item manages a <a href="qwidget.html">QWidget</a>, returns that widget. Otherwise, <code>nullptr</code> is returned.</p> <p><b>Note: </b>While the functions <a href="qlayoutitem.html#layout">layout</a>() and <a href="qlayoutitem.html#spacerItem">spacerItem</a>() perform casts, this function returns another object: <a href="qlayout.html">QLayout</a> and <a href="qspaceritem.html">QSpacerItem</a> inherit <a href="qlayoutitem.html">QLayoutItem</a>, while <a href="qwidget.html">QWidget</a> does not.</p><p><b>See also </b><a href="qlayoutitem.html#layout">layout</a>() and <a href="qlayoutitem.html#spacerItem">spacerItem</a>().</p> <!-- @@@widget --> </div> </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>