<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<!-- customtype.qdoc -->
<title>Custom Type Example | Qt Core 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="qtcore-index.html">Qt Core</a></td><td >Custom Type 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="#overview">Overview</a></li>
<li class="level1"><a href="#the-message-class-definition">The Message Class Definition</a></li>
<li class="level1"><a href="#the-message-class-implementation">The Message Class Implementation</a></li>
<li class="level1"><a href="#using-the-message">Using the Message</a></li>
<li class="level1"><a href="#further-reading">Further Reading</a></li>
</ul>
</div>
<div class="sidebar-content" id="sidebar-content"></div></div>
<h1 class="title">Custom Type Example</h1>
<span class="subtitle"></span>
<!-- $$$tools/customtype-description -->
<div class="descr"> <a name="details"></a>
<p>Contents:</p>
<a name="overview"></a>
<h2 id="overview">Overview</h2>
<p>Qt provides a range of standard value types that are used to provide rich and meaningful APIs. These types are integrated with the meta-object system, enabling them to be stored in <a href="qvariant.html">QVariant</a> objects, written out in debugging information and sent between components in signal-slot communication.</p>
<p>Custom types can also be integrated with the meta-object system as long as they are written to conform to some simple guidelines. In this example, we introduce a simple <code>Message</code> class, we describe how we make it work with <a href="qvariant.html">QVariant</a>, and we show how it can be extended to generate a printable representation of itself for use in debugging output.</p>
<a name="the-message-class-definition"></a>
<h2 id="the-message-class-definition">The Message Class Definition</h2>
<p>The <code>Message</code> class is a simple value class that contains two pieces of information (a <a href="qstring.html">QString</a> and a <a href="qstringlist.html">QStringList</a>), each of which can be read using trivial getter functions:</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 default constructor, copy constructor and destructor are all required, and must be public, if the type is to be integrated into the meta-object system. Other than this, we are free to implement whatever we need to make the type do what we want, so we also include a constructor that lets us set the type's data members.</p>
<p>To enable the type to be used with <a href="qvariant.html">QVariant</a>, we declare it using the <a href="qmetatype.html#Q_DECLARE_METATYPE">Q_DECLARE_METATYPE</a>() macro:</p>
<pre class="cpp">
Q_DECLARE_METATYPE(Message);
</pre>
<p>We do not need to write any additional code to accompany this macro.</p>
<p>To allow us to see a readable description of each <code>Message</code> object when it is sent to the debug output stream, we define a streaming operator:</p>
<pre class="cpp">
<span class="type"><a href="qdebug.html">QDebug</a></span> <span class="keyword">operator</span><span class="operator"><</span><span class="operator"><</span>(<span class="type"><a href="qdebug.html">QDebug</a></span> dbg<span class="operator">,</span> <span class="keyword">const</span> Message <span class="operator">&</span>message);
</pre>
<p>This facility is useful if you need to insert tracing statements in your code for debugging purposes.</p>
<a name="the-message-class-implementation"></a>
<h2 id="the-message-class-implementation">The Message Class Implementation</h2>
<p>The implementation of the default constructor, copy constructor and destructor are straightforward for the <code>Message</code> class:</p>
<pre class="cpp">
Message<span class="operator">::</span>Message()
{
}
Message<span class="operator">::</span>Message(<span class="keyword">const</span> Message <span class="operator">&</span>other)
{
m_body <span class="operator">=</span> other<span class="operator">.</span>m_body;
m_headers <span class="operator">=</span> other<span class="operator">.</span>m_headers;
}
Message<span class="operator">::</span><span class="operator">~</span>Message()
{
}
</pre>
<p>The streaming operator is implemented in the following way:</p>
<pre class="cpp">
<span class="type"><a href="qdebug.html">QDebug</a></span> <span class="keyword">operator</span><span class="operator"><</span><span class="operator"><</span>(<span class="type"><a href="qdebug.html">QDebug</a></span> dbg<span class="operator">,</span> <span class="keyword">const</span> Message <span class="operator">&</span>message)
{
<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> body <span class="operator">=</span> message<span class="operator">.</span>body();
<span class="type"><a href="qvector.html">QVector</a></span><span class="operator"><</span><span class="type"><a href="qstringref.html">QStringRef</a></span><span class="operator">></span> pieces <span class="operator">=</span> body<span class="operator">.</span>splitRef(<span class="string">"\r\n"</span><span class="operator">,</span> <span class="type"><a href="qstring.html">QString</a></span><span class="operator">::</span>SkipEmptyParts);
<span class="keyword">if</span> (pieces<span class="operator">.</span>isEmpty())
dbg<span class="operator">.</span>nospace() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Message()"</span>;
<span class="keyword">else</span> <span class="keyword">if</span> (pieces<span class="operator">.</span>size() <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span>)
dbg<span class="operator">.</span>nospace() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Message("</span> <span class="operator"><</span><span class="operator"><</span> pieces<span class="operator">.</span>first() <span class="operator"><</span><span class="operator"><</span> <span class="string">")"</span>;
<span class="keyword">else</span>
dbg<span class="operator">.</span>nospace() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Message("</span> <span class="operator"><</span><span class="operator"><</span> pieces<span class="operator">.</span>first() <span class="operator"><</span><span class="operator"><</span> <span class="string">" ...)"</span>;
<span class="keyword">return</span> dbg<span class="operator">.</span>maybeSpace();
}
</pre>
<p>Here, we want to represent each value depending on how many lines are stored in the message body. We stream text to the <a href="qdebug.html">QDebug</a> object passed to the operator and return the <a href="qdebug.html">QDebug</a> object obtained from its maybeSpace() member function; this is described in more detail in the <a href="custom-types.html#making-the-type-printable">Creating Custom Qt Types</a> document.</p>
<p>We include the code for the getter functions for completeness:</p>
<pre class="cpp">
<span class="type"><a href="qstring.html">QString</a></span> Message<span class="operator">::</span>body() <span class="keyword">const</span>
{
<span class="keyword">return</span> m_body;
}
<span class="type"><a href="qstringlist.html">QStringList</a></span> Message<span class="operator">::</span>headers() <span class="keyword">const</span>
{
<span class="keyword">return</span> m_headers;
}
</pre>
<p>With the type fully defined, implemented, and integrated with the meta-object system, we can now use it.</p>
<a name="using-the-message"></a>
<h2 id="using-the-message">Using the Message</h2>
<p>In the example's <code>main()</code> function, we show how a <code>Message</code> object can be printed to the console by sending it to the debug stream:</p>
<pre class="cpp">
Message message(body<span class="operator">,</span> headers);
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Original:"</span> <span class="operator"><</span><span class="operator"><</span> message;
</pre>
<p>You can use the type with <a href="qvariant.html">QVariant</a> in exactly the same way as you would use standard Qt value types. Here's how to store a value using the <a href="qvariant.html#setValue">QVariant::setValue</a>() function:</p>
<pre class="cpp">
<span class="type"><a href="qvariant.html">QVariant</a></span> stored;
stored<span class="operator">.</span>setValue(message);
</pre>
<p>Alternatively, the <a href="qvariant.html#fromValue">QVariant::fromValue</a>() and qVariantSetValue() functions can be used if you are using a compiler without support for member template functions.</p>
<p>The value can be retrieved using the <a href="qvariant.html#value">QVariant::value</a>() member template function:</p>
<pre class="cpp">
Message retrieved <span class="operator">=</span> stored<span class="operator">.</span>value<span class="operator"><</span>Message<span class="operator">></span>();
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Retrieved:"</span> <span class="operator"><</span><span class="operator"><</span> retrieved;
retrieved <span class="operator">=</span> qvariant_cast<span class="operator"><</span>Message<span class="operator">></span>(stored);
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Retrieved:"</span> <span class="operator"><</span><span class="operator"><</span> retrieved;
</pre>
<p>Alternatively, the qVariantValue() template function can be used if you are using a compiler without support for member template functions.</p>
<a name="further-reading"></a>
<h2 id="further-reading">Further Reading</h2>
<p>The custom <code>Message</code> type can also be used with direct signal-slot connections.</p>
<p>To register a custom type for use with queued signals and slots, such as those used in cross-thread communication, see the <a href="qtcore-threads-queuedcustomtype-example.html">Queued Custom Type Example</a>.</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>
<p>Files:</p>
<ul>
<li><a href="qtcore-tools-customtype-message-cpp.html">tools/customtype/message.cpp</a></li>
<li><a href="qtcore-tools-customtype-message-h.html">tools/customtype/message.h</a></li>
<li><a href="qtcore-tools-customtype-main-cpp.html">tools/customtype/main.cpp</a></li>
<li><a href="qtcore-tools-customtype-customtype-pro.html">tools/customtype/customtype.pro</a></li>
</ul>
</div>
<!-- @@@tools/customtype -->
</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>
distrib
>
Mageia
>
6
>
armv5tl
>
media
>
core-updates
>
by-pkgid
>
768f7d9f703884aa2562bf0a651086df
>
files
>
786
