<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<!-- schema.qdoc -->
  <title>XML Schema Validation Example | Qt XML Patterns 5.11</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 ><a href="../qtdoc/index.html">Qt 5.11</a></td><td ><a href="qtxmlpatterns-index.html">Qt XML Patterns</a></td><td ><a href="xmlpattern-examples.html">Qt XML Patterns Examples</a></td><td >XML Schema Validation Example</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right">Qt 5.11.2 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="#introduction">Introduction</a></li>
<li class="level2"><a href="#the-user-interface">The User Interface</a></li>
<li class="level2"><a href="#validating-xml-instance-documents">Validating XML Instance Documents</a></li>
<li class="level1"><a href="#code-walk-through">Code Walk-Through</a></li>
<li class="level2"><a href="#the-ui-class-mainwindow">The UI Class: MainWindow</a></li>
</ul>
</div>
<div class="sidebar-content" id="sidebar-content"></div></div>
<h1 class="title">XML Schema Validation Example</h1>
<span class="subtitle"></span>
<!-- $$$schema-brief -->
<p>Using Qt XML Patterns to validate XML with a W3C XML Schema.</p>
<!-- @@@schema -->
<!-- $$$schema-description -->
<div class="descr"> <a name="details"></a>
<p>The XML Schema Validation example shows how to use Qt XML Patterns to validate XML with a W3C XML Schema.</p>
<a name="introduction"></a>
<h2 id="introduction">Introduction</h2>
<p>The example application shows different XML schema definitions and for every definition two XML instance documents, one that is valid according to the schema and one that is not. The user can select the valid or invalid instance document, change it and validate it again.</p>
<a name="the-user-interface"></a>
<h3 >The User Interface</h3>
<p>The UI for this example was created using <a href="../qtdesigner/qtdesigner-manual.html">Qt Designer</a>:</p>
<p class="centerAlign"><img src="images/schema-example.png" alt="" /></p><p>The UI consists of three parts, at the top the XML schema <a href="../qtwidgets/qcombobox.html">selection</a> and the schema <a href="../qtwidgets/qtextbrowser.html">viewer</a>, below the XML instance <a href="../qtwidgets/qcombobox.html">selection</a> and the instance <a href="../qtwidgets/qtextedit.html">editor</a> and at the bottom the validation status <a href="../qtwidgets/qlabel.html">label</a> next to the validation <a href="../qtwidgets/qpushbutton.html">button</a>.</p>
<a name="validating-xml-instance-documents"></a>
<h3 >Validating XML Instance Documents</h3>
<p>You can select one of the three predefined XML schemas and for each schema an valid or invalid instance document. A click on the 'Validate' button will validate the content of the XML instance editor against the schema from the XML schema viewer. As you can modify the content of the instance editor, different instances can be tested and validation error messages analysed.</p>
<a name="code-walk-through"></a>
<h2 id="code-walk-through">Code Walk-Through</h2>
<p>The example's main() function creates the standard instance of <a href="../qtwidgets/qapplication.html">QApplication</a>. Then it creates an instance of the mainwindow class, shows it, and starts the Qt event loop:</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>)
  {
      Q_INIT_RESOURCE(schema);
      <span class="type"><a href="../qtwidgets/qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv);
      MainWindow<span class="operator">*</span> <span class="keyword">const</span> window <span class="operator">=</span> <span class="keyword">new</span> MainWindow;
      window<span class="operator">-</span><span class="operator">&gt;</span>show();
      <span class="keyword">return</span> app<span class="operator">.</span>exec();
  }

</pre>
<a name="the-ui-class-mainwindow"></a>
<h3 >The UI Class: MainWindow</h3>
<p>The example's UI is a conventional Qt GUI application inheriting <a href="../qtwidgets/qmainwindow.html">QMainWindow</a> and the class generated by <a href="../qtdesigner/qtdesigner-manual.html">Qt Designer</a>:</p>
<pre class="cpp">

  <span class="keyword">class</span> MainWindow : <span class="keyword">public</span> <span class="type"><a href="../qtwidgets/qmainwindow.html">QMainWindow</a></span><span class="operator">,</span>
                     <span class="keyword">private</span> Ui<span class="operator">::</span>SchemaMainWindow
  {
      Q_OBJECT

  <span class="keyword">public</span>:
      MainWindow();

  <span class="keyword">private</span> Q_SLOTS:
      <span class="type">void</span> schemaSelected(<span class="type">int</span> index);
      <span class="type">void</span> instanceSelected(<span class="type">int</span> index);
      <span class="type">void</span> validate();
      <span class="type">void</span> textChanged();

  <span class="keyword">private</span>:
      <span class="type">void</span> moveCursor(<span class="type">int</span> line<span class="operator">,</span> <span class="type">int</span> column);
  };

</pre>
<p>The constructor fills the schema and instance <a href="../qtwidgets/qcombobox.html">QComboBox</a> selections with the predefined schemas and instances and connects their <a href="../qtwidgets/qcombobox.html#currentIndexChanged-1">currentIndexChanged()</a> signals to the window's <code>schemaSelected()</code> resp. <code>instanceSelected()</code> slot. Furthermore the signal-slot connections for the validation <a href="../qtwidgets/qpushbutton.html">button</a> and the instance <a href="../qtwidgets/qtextedit.html">editor</a> are set up.</p>
<p>The call to <code>schemaSelected(0)</code> and <code>instanceSelected(0)</code> will trigger the validation of the initial Contact Schema example.</p>
<pre class="cpp">

  MainWindow<span class="operator">::</span>MainWindow()
  {
      setupUi(<span class="keyword">this</span>);

      <span class="keyword">new</span> XmlSyntaxHighlighter(schemaView<span class="operator">-</span><span class="operator">&gt;</span>document());
      <span class="keyword">new</span> XmlSyntaxHighlighter(instanceEdit<span class="operator">-</span><span class="operator">&gt;</span>document());

      schemaSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Contact Schema&quot;</span>));
      schemaSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Recipe Schema&quot;</span>));
      schemaSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Order Schema&quot;</span>));

      instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Valid Contact Instance&quot;</span>));
      instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Invalid Contact Instance&quot;</span>));

      connect(schemaSelection<span class="operator">,</span> SIGNAL(currentIndexChanged(<span class="type">int</span>))<span class="operator">,</span> SLOT(schemaSelected(<span class="type">int</span>)));
      connect(instanceSelection<span class="operator">,</span> SIGNAL(currentIndexChanged(<span class="type">int</span>))<span class="operator">,</span> SLOT(instanceSelected(<span class="type">int</span>)));
      connect(validateButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> SLOT(validate()));
      connect(instanceEdit<span class="operator">,</span> SIGNAL(textChanged())<span class="operator">,</span> SLOT(textChanged()));

      validationStatus<span class="operator">-</span><span class="operator">&gt;</span>setAlignment(<span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>AlignCenter <span class="operator">|</span> <span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>AlignVCenter);

      schemaSelected(<span class="number">0</span>);
      instanceSelected(<span class="number">0</span>);
  }

</pre>
<p>In the <code>schemaSelected()</code> slot the content of the instance <a href="../qtwidgets/qcombobox.html">selection</a> is adapted to the selected schema and the corresponding schema is loaded from the <a href="../qtcore/resources.html">resource file</a> and displayed in the schema <a href="../qtwidgets/qtextbrowser.html">viewer</a>. At the end of the method a revalidation is triggered.</p>
<pre class="cpp">

  <span class="type">void</span> MainWindow<span class="operator">::</span>schemaSelected(<span class="type">int</span> index)
  {
      instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>clear();
      <span class="keyword">if</span> (index <span class="operator">=</span><span class="operator">=</span> <span class="number">0</span>) {
          instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Valid Contact Instance&quot;</span>));
          instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Invalid Contact Instance&quot;</span>));
      } <span class="keyword">else</span> <span class="keyword">if</span> (index <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span>) {
          instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Valid Recipe Instance&quot;</span>));
          instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Invalid Recipe Instance&quot;</span>));
      } <span class="keyword">else</span> <span class="keyword">if</span> (index <span class="operator">=</span><span class="operator">=</span> <span class="number">2</span>) {
          instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Valid Order Instance&quot;</span>));
          instanceSelection<span class="operator">-</span><span class="operator">&gt;</span>addItem(tr(<span class="string">&quot;Invalid Order Instance&quot;</span>));
      }
      textChanged();

      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> fileName <span class="operator">=</span> <span class="type"><a href="../qtcore/qstring.html#QStringLiteral">QStringLiteral</a></span>(<span class="string">&quot;:/schema_&quot;</span>)
          <span class="operator">+</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span><span class="operator">::</span>number(index) <span class="operator">+</span> <span class="type"><a href="../qtcore/qstring.html#QStringLiteral">QStringLiteral</a></span>(<span class="string">&quot;.xsd&quot;</span>);
      <span class="type"><a href="../qtcore/qfile.html">QFile</a></span> schemaFile(fileName);
      <span class="keyword">if</span> (<span class="operator">!</span>schemaFile<span class="operator">.</span>open(<span class="type"><a href="../qtcore/qiodevice.html">QIODevice</a></span><span class="operator">::</span>ReadOnly)) {
          <a href="../qtcore/qtglobal.html#qWarning">qWarning</a>() <span class="operator">&lt;</span><span class="operator">&lt;</span> <span class="string">&quot;Cannot open&quot;</span> <span class="operator">&lt;</span><span class="operator">&lt;</span> <span class="type"><a href="../qtcore/qdir.html">QDir</a></span><span class="operator">::</span>toNativeSeparators(fileName)
              <span class="operator">&lt;</span><span class="operator">&lt;</span> <span class="char">':'</span> <span class="operator">&lt;</span><span class="operator">&lt;</span> schemaFile<span class="operator">.</span>errorString();
          <span class="keyword">return</span>;
      }

      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> schemaText(<span class="type"><a href="../qtcore/qstring.html">QString</a></span><span class="operator">::</span>fromUtf8(schemaFile<span class="operator">.</span>readAll()));
      schemaView<span class="operator">-</span><span class="operator">&gt;</span>setPlainText(schemaText);

      validate();
  }

</pre>
<p>In the <code>instanceSelected()</code> slot the selected instance is loaded from the <a href="../qtcore/resources.html">resource file</a> and loaded into the instance <a href="../qtwidgets/qtextedit.html">editor</a> an the revalidation is triggered again.</p>
<pre class="cpp">

  <span class="type">void</span> MainWindow<span class="operator">::</span>instanceSelected(<span class="type">int</span> index)
  {
      <span class="keyword">if</span> (index <span class="operator">&lt;</span> <span class="number">0</span>) {
          instanceEdit<span class="operator">-</span><span class="operator">&gt;</span>setPlainText(<span class="type"><a href="../qtcore/qstring.html">QString</a></span>());
          <span class="keyword">return</span>;
      }
      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> fileName <span class="operator">=</span> <span class="type"><a href="../qtcore/qstring.html#QStringLiteral">QStringLiteral</a></span>(<span class="string">&quot;:/instance_&quot;</span>)
          <span class="operator">+</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span><span class="operator">::</span>number(<span class="number">2</span> <span class="operator">*</span> schemaSelection<span class="operator">-</span><span class="operator">&gt;</span>currentIndex() <span class="operator">+</span> index)
          <span class="operator">+</span> <span class="type"><a href="../qtcore/qstring.html#QStringLiteral">QStringLiteral</a></span>(<span class="string">&quot;.xml&quot;</span>);
      <span class="type"><a href="../qtcore/qfile.html">QFile</a></span> instanceFile(fileName);
      <span class="keyword">if</span> (<span class="operator">!</span>instanceFile<span class="operator">.</span>open(<span class="type"><a href="../qtcore/qiodevice.html">QIODevice</a></span><span class="operator">::</span>ReadOnly)) {
          <a href="../qtcore/qtglobal.html#qWarning">qWarning</a>() <span class="operator">&lt;</span><span class="operator">&lt;</span> <span class="string">&quot;Cannot open&quot;</span> <span class="operator">&lt;</span><span class="operator">&lt;</span> <span class="type"><a href="../qtcore/qdir.html">QDir</a></span><span class="operator">::</span>toNativeSeparators(fileName)
              <span class="operator">&lt;</span><span class="operator">&lt;</span> <span class="char">':'</span> <span class="operator">&lt;</span><span class="operator">&lt;</span> instanceFile<span class="operator">.</span>errorString();
          <span class="keyword">return</span>;
      }
      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> instanceText(<span class="type"><a href="../qtcore/qstring.html">QString</a></span><span class="operator">::</span>fromUtf8(instanceFile<span class="operator">.</span>readAll()));
      instanceEdit<span class="operator">-</span><span class="operator">&gt;</span>setPlainText(instanceText);

      validate();
  }

</pre>
<p>The <code>validate()</code> slot does the actual work in this example. At first it stores the content of the schema <a href="../qtwidgets/qtextbrowser.html">viewer</a> and the <a href="../qtwidgets/qtextedit.html">editor</a> into temporary <a href="../qtcore/qbytearray.html">variables</a>. Then it instanciates a <code>MessageHandler</code> object which inherits from <a href="qabstractmessagehandler.html">QAbstractMessageHandler</a> and is a convenience class to store error messages from the XmlPatterns system.</p>
<pre class="cpp">

  <span class="keyword">class</span> MessageHandler : <span class="keyword">public</span> <span class="type"><a href="qabstractmessagehandler.html">QAbstractMessageHandler</a></span>
  {
  <span class="keyword">public</span>:
      MessageHandler()
          : <span class="type"><a href="qabstractmessagehandler.html">QAbstractMessageHandler</a></span>(<span class="number">0</span>)
      {
      }

      <span class="type"><a href="../qtcore/qstring.html">QString</a></span> statusMessage() <span class="keyword">const</span>
      {
          <span class="keyword">return</span> m_description;
      }

      <span class="type">int</span> line() <span class="keyword">const</span>
      {
          <span class="keyword">return</span> m_sourceLocation<span class="operator">.</span>line();
      }

      <span class="type">int</span> column() <span class="keyword">const</span>
      {
          <span class="keyword">return</span> m_sourceLocation<span class="operator">.</span>column();
      }

  <span class="keyword">protected</span>:
      <span class="keyword">virtual</span> <span class="type">void</span> handleMessage(<span class="type"><a href="../qtcore/qtglobal.html#QtMsgType-enum">QtMsgType</a></span> type<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&amp;</span>description<span class="operator">,</span>
                                 <span class="keyword">const</span> <span class="type"><a href="../qtcore/qurl.html">QUrl</a></span> <span class="operator">&amp;</span>identifier<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qsourcelocation.html">QSourceLocation</a></span> <span class="operator">&amp;</span>sourceLocation)
      {
          Q_UNUSED(type);
          Q_UNUSED(identifier);

          m_description <span class="operator">=</span> description;
          m_sourceLocation <span class="operator">=</span> sourceLocation;
      }

  <span class="keyword">private</span>:
      <span class="type"><a href="../qtcore/qstring.html">QString</a></span> m_description;
      <span class="type"><a href="qsourcelocation.html">QSourceLocation</a></span> m_sourceLocation;
  };

</pre>
<p>After the <a href="qxmlschema.html">QXmlSchema</a> is instanciated and the message handler set on it, the <a href="qxmlschema.html#load">load()</a> method is called with the schema data as argument. If the schema is invalid or a parsing error has occurred, <a href="qxmlschema.html#isValid">isValid()</a> returns <code>false</code> and the error is flagged in <code>errorOccurred</code>. If the loading was successful, a <a href="qxmlschemavalidator.html">QXmlSchemaValidator</a> is instanciated and the schema passed in the constructor. A call to <a href="qxmlschemavalidator.html#validate">validate()</a> will validate the passed XML instance data against the XML schema. The return value of that method signals whether the validation was successful. Depending on the success the status <a href="../qtwidgets/qlabel.html">label</a> is set to 'validation successful' or the error message stored in the <code>MessageHandler</code></p>
<p>The rest of the code does only some fancy coloring and eyecandy.</p>
<pre class="cpp">

  <span class="type">void</span> MainWindow<span class="operator">::</span>validate()
  {
      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qbytearray.html">QByteArray</a></span> schemaData <span class="operator">=</span> schemaView<span class="operator">-</span><span class="operator">&gt;</span>toPlainText()<span class="operator">.</span>toUtf8();
      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qbytearray.html">QByteArray</a></span> instanceData <span class="operator">=</span> instanceEdit<span class="operator">-</span><span class="operator">&gt;</span>toPlainText()<span class="operator">.</span>toUtf8();

      MessageHandler messageHandler;

      <span class="type"><a href="qxmlschema.html">QXmlSchema</a></span> schema;
      schema<span class="operator">.</span>setMessageHandler(<span class="operator">&amp;</span>messageHandler);

      schema<span class="operator">.</span>load(schemaData);

      bool errorOccurred <span class="operator">=</span> <span class="keyword">false</span>;
      <span class="keyword">if</span> (<span class="operator">!</span>schema<span class="operator">.</span>isValid()) {
          errorOccurred <span class="operator">=</span> <span class="keyword">true</span>;
      } <span class="keyword">else</span> {
          <span class="type"><a href="qxmlschemavalidator.html">QXmlSchemaValidator</a></span> validator(schema);
          <span class="keyword">if</span> (<span class="operator">!</span>validator<span class="operator">.</span>validate(instanceData))
              errorOccurred <span class="operator">=</span> <span class="keyword">true</span>;
      }

      <span class="keyword">if</span> (errorOccurred) {
          validationStatus<span class="operator">-</span><span class="operator">&gt;</span>setText(messageHandler<span class="operator">.</span>statusMessage());
          moveCursor(messageHandler<span class="operator">.</span>line()<span class="operator">,</span> messageHandler<span class="operator">.</span>column());
      } <span class="keyword">else</span> {
          validationStatus<span class="operator">-</span><span class="operator">&gt;</span>setText(tr(<span class="string">&quot;validation successful&quot;</span>));
      }

      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> styleSheet <span class="operator">=</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span>(<span class="string">&quot;QLabel {background: %1; padding: 3px}&quot;</span>)
                                        <span class="operator">.</span>arg(errorOccurred <span class="operator">?</span> <span class="type">QColor</span>(<span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>red)<span class="operator">.</span>lighter(<span class="number">160</span>)<span class="operator">.</span>name() :
                                                             <span class="type">QColor</span>(<span class="type"><a href="../qtcore/qt.html">Qt</a></span><span class="operator">::</span>green)<span class="operator">.</span>lighter(<span class="number">160</span>)<span class="operator">.</span>name());
      validationStatus<span class="operator">-</span><span class="operator">&gt;</span>setStyleSheet(styleSheet);
  }

</pre>
<p>Files:</p>
<ul>
<li><a href="qtxmlpatterns-schema-files-invalid-contact-xml.html">schema/files/invalid_contact.xml</a></li>
<li><a href="qtxmlpatterns-schema-files-invalid-order-xml.html">schema/files/invalid_order.xml</a></li>
<li><a href="qtxmlpatterns-schema-files-invalid-recipe-xml.html">schema/files/invalid_recipe.xml</a></li>
<li><a href="qtxmlpatterns-schema-files-valid-contact-xml.html">schema/files/valid_contact.xml</a></li>
<li><a href="qtxmlpatterns-schema-files-valid-order-xml.html">schema/files/valid_order.xml</a></li>
<li><a href="qtxmlpatterns-schema-files-valid-recipe-xml.html">schema/files/valid_recipe.xml</a></li>
<li><a href="qtxmlpatterns-schema-main-cpp.html">schema/main.cpp</a></li>
<li><a href="qtxmlpatterns-schema-mainwindow-cpp.html">schema/mainwindow.cpp</a></li>
<li><a href="qtxmlpatterns-schema-mainwindow-h.html">schema/mainwindow.h</a></li>
<li><a href="qtxmlpatterns-schema-schema-pro.html">schema/schema.pro</a></li>
<li><a href="qtxmlpatterns-schema-schema-qrc.html">schema/schema.qrc</a></li>
<li><a href="qtxmlpatterns-schema-schema-ui.html">schema/schema.ui</a></li>
</ul>
</div>
<!-- @@@schema -->
        </div>
       </div>
   </div>
   </div>
</div>
<div class="footer">
   <p>
   <acronym title="Copyright">&copy;</acronym> 2018 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>