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<td >Qt 5.9</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">Qt 5.9.4 Reference Documentation</td>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#public-functions">Public Functions</a></li>
<li class="level1"><a href="#details">Detailed Description</a></li>
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<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 -->
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<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign">   <span class="preprocessor">#include &lt;QLayoutItem&gt;</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> = Qt::Alignment())</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>(int <i>w</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 &amp;<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="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> = Qt::Alignment())</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>(<span class="type">int</span> <i>w</i>) const</h3>
<p>Returns the preferred height for this layout item, given the width <i>w</i>.</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 &quot;mutable&quot;</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">&gt;</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&#x2e; 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> &amp;<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 -->
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