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<title>Qt 4.8: Custom Type Sending Example</title>
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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="#overview">Overview</a></li>
<li class="level1"><a href="#the-window-and-message-class-definitions">The Window and Message Class Definitions</a></li>
<li class="level1"><a href="#the-window-class-implementation">The Window Class Implementation</a></li>
<li class="level1"><a href="#making-the-connection">Making the Connection</a></li>
<li class="level1"><a href="#further-reading">Further Reading</a></li>
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<h1 class="title">Custom Type Sending Example</h1>
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<!-- $$$tools/customtypesending-description -->
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<p>Files:</p>
<ul>
<li><a href="tools-customtypesending-message-cpp.html">tools/customtypesending/message.cpp</a></li>
<li><a href="tools-customtypesending-message-h.html">tools/customtypesending/message.h</a></li>
<li><a href="tools-customtypesending-window-cpp.html">tools/customtypesending/window.cpp</a></li>
<li><a href="tools-customtypesending-window-h.html">tools/customtypesending/window.h</a></li>
<li><a href="tools-customtypesending-main-cpp.html">tools/customtypesending/main.cpp</a></li>
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<p>The Custom Type Sending example shows how to use a custom type with signals and slots.<p class="centerAlign"><img src="images/customtypesending-example.png" alt="" /></p><a name="overview"></a>
<h2>Overview</h2>
<p>In the <a href="tools-customtype.html">Custom Type Example</a>, we showed how to integrate custom types with the meta-object system, enabling them to be stored in <a href="qvariant.html">QVariant</a> objects, written out in debugging information and used in signal-slot communication.</p>
<p>In this example, we demonstrate that the preparations made to the <tt>Message</tt> class and its declaration with <a href="qmetatype.html#Q_DECLARE_METATYPE">Q_DECLARE_METATYPE</a>() enable it to be used with direct signal-slot connections. We do this by creating a <tt>Window</tt> class containing signals and slots whose signatures include <tt>Message</tt> arguments.</p>
<a name="the-window-and-message-class-definitions"></a>
<h2>The Window and Message Class Definitions</h2>
<p>We define a simple <tt>Window</tt> class with a signal and public slot that allow a <tt>Message</tt> object to be sent via a signal-slot connection:</p>
<pre class="cpp"> <span class="keyword">class</span> Window : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span>
{
Q_OBJECT
<span class="keyword">public</span>:
Window();
<span class="keyword">signals</span>:
<span class="type">void</span> messageSent(<span class="keyword">const</span> Message <span class="operator">&</span>message);
<span class="keyword">public</span> <span class="keyword">slots</span>:
<span class="type">void</span> setMessage(<span class="keyword">const</span> Message <span class="operator">&</span>message);
<span class="keyword">private</span> <span class="keyword">slots</span>:
<span class="type">void</span> sendMessage();
<span class="keyword">private</span>:
Message thisMessage;
<span class="type"><a href="qtextedit.html">QTextEdit</a></span> <span class="operator">*</span>editor;
};</pre>
<p>The window will contain a text editor to show the contents of a message and a push button that the user can click to send a message. To facilitate this, we also define the <tt>sendMessage()</tt> slot. We also keep a <tt>Message</tt> instance in the <tt>thisMessage</tt> private variable which holds the actual message to be sent.</p>
<p>The <tt>Message</tt> class is defined in the following way:</p>
<pre class="cpp"> <span class="keyword">class</span> Message
{
<span class="keyword">public</span>:
Message();
Message(<span class="keyword">const</span> Message <span class="operator">&</span>other);
<span class="operator">~</span>Message();
Message(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>body<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstringlist.html">QStringList</a></span> <span class="operator">&</span>headers);
<span class="type"><a href="qstring.html">QString</a></span> body() <span class="keyword">const</span>;
<span class="type"><a href="qstringlist.html">QStringList</a></span> headers() <span class="keyword">const</span>;
<span class="keyword">private</span>:
<span class="type"><a href="qstring.html">QString</a></span> m_body;
<span class="type"><a href="qstringlist.html">QStringList</a></span> m_headers;
};</pre>
<p>The type is declared to the meta-type system with the <a href="qmetatype.html#Q_DECLARE_METATYPE">Q_DECLARE_METATYPE</a>() macro:</p>
<pre class="cpp"> <a href="qmetatype.html#Q_DECLARE_METATYPE">Q_DECLARE_METATYPE</a>(Message);</pre>
<p>This will make the type available for use in direct signal-slot connections.</p>
<a name="the-window-class-implementation"></a>
<h2>The Window Class Implementation</h2>
<p>The <tt>Window</tt> constructor sets up a user interface containing a text editor and a push button.</p>
<pre class="cpp"> Window<span class="operator">::</span>Window()
{
editor <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtextedit.html">QTextEdit</a></span>();
<span class="type"><a href="qpushbutton.html">QPushButton</a></span> <span class="operator">*</span>sendButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpushbutton.html">QPushButton</a></span>(tr(<span class="string">"&Send message"</span>));
connect(sendButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(sendMessage()));
<span class="type"><a href="qhboxlayout.html">QHBoxLayout</a></span> <span class="operator">*</span>buttonLayout <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qhboxlayout.html">QHBoxLayout</a></span>();
buttonLayout<span class="operator">-</span><span class="operator">></span>addStretch();
buttonLayout<span class="operator">-</span><span class="operator">></span>addWidget(sendButton);
buttonLayout<span class="operator">-</span><span class="operator">></span>addStretch();
<span class="type"><a href="qvboxlayout.html">QVBoxLayout</a></span> <span class="operator">*</span>layout <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qvboxlayout.html">QVBoxLayout</a></span>(<span class="keyword">this</span>);
layout<span class="operator">-</span><span class="operator">></span>addWidget(editor);
layout<span class="operator">-</span><span class="operator">></span>addLayout(buttonLayout);
setWindowTitle(tr(<span class="string">"Custom Type Sending"</span>));
}</pre>
<p>The button's <a href="qabstractbutton.html#clicked">clicked()</a> signal is connected to the window's <tt>sendMessage()</tt> slot, which emits the <tt>messageSent(Message)</tt> signal with the <tt>Message</tt> held by the <tt>thisMessage</tt> variable:</p>
<pre class="cpp"> <span class="type">void</span> Window<span class="operator">::</span>sendMessage()
{
thisMessage <span class="operator">=</span> Message(editor<span class="operator">-</span><span class="operator">></span>toPlainText()<span class="operator">,</span> thisMessage<span class="operator">.</span>headers());
<span class="keyword">emit</span> messageSent(thisMessage);
}</pre>
<p>We implement a slot to allow the message to be received, and this also lets us set the message in the window programatically:</p>
<pre class="cpp"> <span class="type">void</span> Window<span class="operator">::</span>setMessage(<span class="keyword">const</span> Message <span class="operator">&</span>message)
{
thisMessage <span class="operator">=</span> message;
editor<span class="operator">-</span><span class="operator">></span>setPlainText(thisMessage<span class="operator">.</span>body());
}</pre>
<p>In this function, we simply assign the new message to <tt>thisMessage</tt> and update the text in the editor.</p>
<a name="making-the-connection"></a>
<h2>Making the Connection</h2>
<p>In the example's <tt>main()</tt> function, we perform the connection between two instances of the <tt>Window</tt> class:</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);
Window window1;
<span class="type"><a href="qstringlist.html">QStringList</a></span> headers;
headers <span class="operator"><</span><span class="operator"><</span> <span class="string">"Subject: Hello World"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"From: qt-info@nokia.com"</span>;
<span class="type"><a href="qstring.html">QString</a></span> body <span class="operator">=</span> <span class="string">"This is a test.\r\n"</span>;
Message message(body<span class="operator">,</span> headers);
window1<span class="operator">.</span>setMessage(message);
Window window2;
<span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>connect(<span class="operator">&</span>window1<span class="operator">,</span> SIGNAL(messageSent(Message))<span class="operator">,</span>
<span class="operator">&</span>window2<span class="operator">,</span> SLOT(setMessage(Message)));
<span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>connect(<span class="operator">&</span>window2<span class="operator">,</span> SIGNAL(messageSent(Message))<span class="operator">,</span>
<span class="operator">&</span>window1<span class="operator">,</span> SLOT(setMessage(Message)));
window1<span class="operator">.</span>show();
window2<span class="operator">.</span>show();
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>We set the message for the first window and connect the <tt>messageSent(Message)</tt> signal from each window to the other's <tt>setMessage(Message)</tt> slot. Since the signals and slots mechanism is only concerned with the type, we can simplify the signatures of both the signal and slot when we make the connection.</p>
<p>When the user clicks on the <b>Send message</b> button in either window, the message shown will be emitted in a signal that the other window will receive and display.</p>
<a name="further-reading"></a>
<h2>Further Reading</h2>
<p>Although the custom <tt>Message</tt> type can be used with direct signals and slots, an additional registration step needs to be performed if you want to use it with queued signal-slot connections. See the <a href="threads-queuedcustomtype.html">Queued Custom Type Example</a> for details.</p>
<p>More information on using custom types with Qt can be found in the <a href="custom-types.html">Creating Custom Qt Types</a> document.</p>
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