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    <title>Loading Documents</title>
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  <td width="1">&nbsp;&nbsp;</td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a></td>
  </tr></table><h1 class="title">Loading Documents<br /><span class="subtitle"></span>
  </h1>
  <p>The application in this example loads or prints the documents passed as commandline parameters to further instances of this application.</p>
  <pre><span class="comment"> /****************************************************************************
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   #include &lt;qtsingleapplication.h&gt;
   #include &lt;QtCore/QFile&gt;
   #include &lt;QtGui/QMainWindow&gt;
   #include &lt;QtGui/QPrinter&gt;
   #include &lt;QtGui/QPainter&gt;
   #include &lt;QtGui/QTextEdit&gt;
   #include &lt;QtGui/QMdiArea&gt;
   #include &lt;QtCore/QTextStream&gt;
  
   class MainWindow : public QMainWindow
   {
       Q_OBJECT
   public:
       MainWindow();
  
   public slots:
       void handleMessage(const QString&amp; message);
  
   signals:
       void needToShow();
  
   private:
       QMdiArea *workspace;
   };</pre>
  <p>The user interface in this application is a <a href="http://qt.nokia.com/doc/4.5/qmainwindow.html">QMainWindow</a> subclass with a <a href="http://qt.nokia.com/doc/4.5/qmdiarea.html">QMdiArea</a> as the central widget. It implements a slot <tt>handleMessage()</tt> that will be connected to the messageReceived() signal of the <a href="qtsingleapplication.html">QtSingleApplication</a> class.</p>
  <pre> MainWindow::MainWindow()
   {
       workspace = new QMdiArea(this);
  
       setCentralWidget(workspace);
   }</pre>
  <p>The <a href="http://qt.nokia.com/doc/4.5/designer-to-know.html">MainWindow</a> constructor creates a minimal user interface.</p>
  <pre> void MainWindow::handleMessage(const QString&amp; message)
   {
       enum Action {
           Nothing,
           Open,
           Print
       } action;
  
       action = Nothing;
       QString filename = message;
       if (message.toLower().startsWith(&quot;/print &quot;)) {
           filename = filename.mid(7);
           action = Print;
       } else if (!message.isEmpty()) {
           action = Open;
       }
       if (action == Nothing) {
           emit needToShow();
           return;
       }
  
       QFile file(filename);
       QString contents;
       if (file.open(QIODevice::ReadOnly))
           contents = file.readAll();
       else
           contents = &quot;[[Error: Could not load file &quot; + filename + &quot;]]&quot;;
  
       QTextEdit *view = new QTextEdit;
       view-&gt;setPlainText(contents);
  
       switch(action) {</pre>
  <p>The handleMessage() slot interprets the message passed in as a filename that can be prepended with <i>/print</i> to indicate that the file should just be printed rather than loaded.</p>
  <pre>     case Print:
           {
               QPrinter printer;
               view-&gt;print(&amp;printer);
               delete view;
           }
           break;
  
       case Open:
           {
               workspace-&gt;addSubWindow(view);
               view-&gt;setWindowTitle(message);
               view-&gt;show();
               emit needToShow();
           }
           break;
       default:
           break;
       };
   }</pre>
  <p>Loading the file will also activate the window.</p>
  <pre> #include &quot;main.moc&quot;
  
   int main(int argc, char **argv)
   {
       QtSingleApplication instance(&quot;File loader QtSingleApplication example&quot;, argc, argv);
       QString message;
       for (int a = 1; a &lt; argc; ++a) {
           message += argv[a];
           if (a &lt; argc-1)
               message += &quot; &quot;;
       }
  
       if (instance.sendMessage(message))
           return 0;</pre>
  <p>The <tt>main</tt> entry point function creates a <a href="qtsingleapplication.html">QtSingleApplication</a> object, and creates a message to send to a running instance of the application. If the message was sent successfully the process exits immediately.</p>
  <pre>     MainWindow mw;
       mw.handleMessage(message);
       mw.show();
  
       QObject::connect(&amp;instance, SIGNAL(messageReceived(const QString&amp;)),
                        &amp;mw, SLOT(handleMessage(const QString&amp;)));
  
       instance.setActivationWindow(&amp;mw, false);
       QObject::connect(&amp;mw, SIGNAL(needToShow()), &amp;instance, SLOT(activateWindow()));
  
       return instance.exec();
   }</pre>
  <p>If the message could not be sent the application starts up. Note that <tt>false</tt> is passed to the call to setActivationWindow() to prevent automatic activation for every message received, e.g&#x2e; when the application should just print a file. Instead, the message handling function determines whether activation is requested, and signals that by emitting the needToShow() signal. This is then simply connected directly to <a href="qtsingleapplication.html">QtSingleApplication</a>'s activateWindow() slot.</p>
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