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</tr></table><h1 class="title">Loading Documents<br /><span class="subtitle"></span>
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<p>The application in this example loads or prints the documents passed as commandline parameters to further instances of this application.</p>
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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/4.6/qmainwindow.html">QMainWindow</a> subclass with a <a href="http://qt.nokia.com/doc/4.6/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/4.6/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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