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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#calculatorform-definition">CalculatorForm Definition</a></li>
<li class="level1"><a href="#calculatorform-implementation">CalculatorForm Implementation</a></li>
<li class="level1"><a href="#function"><tt>main()</tt> Function</a></li>
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<h1 class="title">Multiple Inheritance Example</h1>
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<p>Files:</p>
<ul>
<li><a href="uitools-multipleinheritance-calculatorform-cpp.html">uitools/multipleinheritance/calculatorform.cpp</a></li>
<li><a href="uitools-multipleinheritance-calculatorform-h.html">uitools/multipleinheritance/calculatorform.h</a></li>
<li><a href="uitools-multipleinheritance-calculatorform-ui.html">uitools/multipleinheritance/calculatorform.ui</a></li>
<li><a href="uitools-multipleinheritance-main-cpp.html">uitools/multipleinheritance/main.cpp</a></li>
<li><a href="uitools-multipleinheritance-multipleinheritance-pro.html">uitools/multipleinheritance/multipleinheritance.pro</a></li>
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<p>The Multiple Inheritance Example shows how to use a form created with <i>Qt Designer</i> in an application by subclassing both <a href="qwidget.html">QWidget</a> and the user interface class, which is <tt>Ui::CalculatorForm</tt>.<p class="centerAlign"><img src="images/multipleinheritance-example.png" alt="" /></p><p>To subclass the <tt>calculatorform.ui</tt> file and ensure that <tt>qmake</tt> processes it with the <tt>uic</tt>, we have to include <tt>calculatorform.ui</tt> in the <tt>.pro</tt> file, as shown below:</p>
<pre class="cpp"> SOURCES = calculatorform.cpp main.cpp
HEADERS = calculatorform.h
FORMS = calculatorform.ui</pre>
<p>When the project is compiled, the <tt>uic</tt> will generate a corresponding <tt>ui_calculatorform.h</tt>.</p>
<a name="calculatorform-definition"></a>
<h2>CalculatorForm Definition</h2>
<p>In the <tt>CalculatorForm</tt> definition, we include the <tt>ui_calculatorform.h</tt> that was generated earlier.</p>
<pre class="cpp"> <span class="preprocessor">#include "ui_calculatorform.h"</span></pre>
<p>As mentioned earlier, the class is a subclass of both <a href="qwidget.html">QWidget</a> and <tt>Ui::CalculatorForm</tt>.</p>
<pre class="cpp"> <span class="keyword">class</span> CalculatorForm : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span><span class="operator">,</span> <span class="keyword">private</span> Ui<span class="operator">::</span>CalculatorForm
{
Q_OBJECT
<span class="keyword">public</span>:
CalculatorForm(<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">private</span> <span class="keyword">slots</span>:
<span class="type">void</span> on_inputSpinBox1_valueChanged(<span class="type">int</span> value);
<span class="type">void</span> on_inputSpinBox2_valueChanged(<span class="type">int</span> value);
};</pre>
<p>Two slots are defined according to the <a href="designer-using-a-ui-file.html#automatic-connections">automatic connection</a> naming convention required by <tt>uic</tt>. This is to ensure that <a href="qmetaobject.html">QMetaObject</a>'s auto-connection facilities connect all the signals and slots involved automatically.</p>
<a name="calculatorform-implementation"></a>
<h2>CalculatorForm Implementation</h2>
<p>In the constructor, we call <tt>setupUi()</tt> to load the user interface file. Note that we do not need the <tt>ui</tt> prefix as <tt>CalculatorForm</tt> is a subclass of the user interface class.</p>
<pre class="cpp"> CalculatorForm<span class="operator">::</span>CalculatorForm(<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)
{
setupUi(<span class="keyword">this</span>);
}</pre>
<p>We include two slots, <tt>on_inputSpinBox1_valueChanged()</tt> and <tt>on_inputSpinBox2_valueChanged()</tt>. These slots respond to the <a href="qspinbox.html#valueChanged">valueChanged()</a> signal that both spin boxes emit. Whenever there is a change in one spin box's value, we take that value and add it to whatever value the other spin box has.</p>
<pre class="cpp"> <span class="type">void</span> CalculatorForm<span class="operator">::</span>on_inputSpinBox1_valueChanged(<span class="type">int</span> value)
{
outputWidget<span class="operator">-</span><span class="operator">></span>setText(<span class="type"><a href="qstring.html">QString</a></span><span class="operator">::</span>number(value <span class="operator">+</span> inputSpinBox2<span class="operator">-</span><span class="operator">></span>value()));
}
<span class="type">void</span> CalculatorForm<span class="operator">::</span>on_inputSpinBox2_valueChanged(<span class="type">int</span> value)
{
outputWidget<span class="operator">-</span><span class="operator">></span>setText(<span class="type"><a href="qstring.html">QString</a></span><span class="operator">::</span>number(value <span class="operator">+</span> inputSpinBox1<span class="operator">-</span><span class="operator">></span>value()));
}</pre>
<a name="function"></a>
<h2><tt>main()</tt> Function</h2>
<p>The <tt>main()</tt> function instantiates <a href="qapplication.html">QApplication</a> and <tt>CalculatorForm</tt>. The <tt>calculator</tt> object is displayed by invoking the <a href="qwidget.html#show">show()</a> 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);
CalculatorForm calculator;
<span class="preprocessor">#if defined(Q_OS_SYMBIAN)</span>
calculator<span class="operator">.</span>showMaximized();
<span class="preprocessor">#else</span>
calculator<span class="operator">.</span>show();
<span class="preprocessor">#endif</span>
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>There are various approaches to include forms into applications. The Multiple Inheritance approach is just one of them. See <a href="designer-using-a-ui-file.html">Using a Designer UI File in Your Application</a> for more information on the other approaches available.</p>
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